DESCRIPTION PROPYLENE-BASED BLOCK COPOLYMER, COMPOSITION CONTAINING THE COPOLYMER, AND MOLDED PRODUCTS OBTAINED THEREFROM Technical Field [0001] The present invention relates to a propylene-based block copolymer, a composition containing the copolymer and molded products obtained therefrom. More particularly, the present invention relates to a propylene-based block copolymer having excellent balance between rigidity and impact resistance, good molding processability and extremely excellent appearance properties in the molding process, a composition containing the copolymer and molded products obtained therefrom. Background Art [0002] Propylene-based polymers are generally widely utilized for automotive interior trim or automotive exterior trim such as fender, bumper, side molding, mud guard and mirror cover by subjecting the polymers to injection molding, because of their excellent rigidity, hardness and heat resistance. [0003] Moreover, a polypropylene composition having been improved in impact resistance by adding polyethylene, a rubber component, a non-crystalline or low-crystalline ethylene/propylene copolymer (EPR), a non-crystalline ethylene/a-olefin copolymer or the like to a propylene-based polymer or by directly polymerizing them according to the use purpose and a polypropylene composition to which an inorganic filler such as talc has been further added in order to make up for rigidity lowered by blending the rubber component are also well known. In the case of such propylene-based polymers, however, further weight-lightening and wall-thinning of their molded articles have been desired, and in order to obtain molded articles not only realizing them but also having sufficient strength, a propylene-based polymer having more improved balance between rigidity and impact resistance (that is, excellent in both of rigidity and impact resistance) or a composition comprising the polymer has been desired. Furthermore, a propylene-based polymer capable of improving a molded product appearance defect called "flow mark" caused by irregular flow of a molten resin formed in the molding process or a composition comprising the polymer has been also desired. [0004] As a means to solve such a problem, a technique of widening a molecular weight distribution of a propylene-based polymer is generally known. In particular, a propylene-based polymer containing a high-molecular weight component exerts an excellent effect. In the past, there have beenmade a large number of reports that the balance between rigidity and impact resistance has been improved by, for example, a method wherein a polymer having different molecular weights is prepared by multi-stage polymerization to widen a molecular weight distribution of the polymer (Japanese Patent Laid-Open Publication No. 170843/1993 (patent literature 1) ) , a method wherein a catalyst containing plural kinds of electron donors is used (Japanese Patent Laid-Open Publication No. 7703/1991 (patent literature 2)), and a method wherein an olefin polymerization catalyst using a solid titanium catalyst component and using an aluminum alkyl compound and a nitrogen-containing aliphatic silicon compound as co-catalysts (Japanese Patent Laid-Open Publication No. 120021/1996 (patent literature 3)) is used to widen a molecular weight distribution. Moreover, a method wherein various propylene resin compositions are mixed to improve appearance properties with maintaining rigidity and impact resistance (Japanese Patent Laid-Open PublicationNo. 163120/2008 (patent literature 4) ), etc. have been also reported. Furthermore, there have been made a large number of reports that a titanium trichloride catalyst (TiCl3) hitherto well known is also a catalyst capable of achieving widening of a molecular weight distribution (Japanese Patent Laid-Open Publication No. 34478/1972 (patent literature 5)). [0005] In the patent literatures 1 and2, however, the molded product appearance has not been improved though the balance between rigidity and impact resistance has been improved. In the patent literature 3, improvement in flow mark of molded product appearance is insufficient. In the patent literature 4, flow mark of molded product appearance is improved, but the propylene/ethylene rubber component of a high molecular weight is aggregated to sometimes cause a defect of graininess on the molded product surface. In the patent literature 5, widening of a molecular weight distribution can be achieved by taking advantage of features of the catalyst, but because of a large amount of a residual metal due to low activity of the catalyst, deashing step is necessary, or because of extremely low streoregularity, there is a disadvantage that rigidity cannot be increased. [0006] The present invention has been made in view of such prior art as mentioned above, and it is an object of the present invention to obtain, withahighactivity, apropylene-based polymer which is excellent in both of rigidity and impact resistance and is very excellent also in its molded product appearance and to provide a composition containing the polymer and molded products obtained therefrom. Citation List Patent Literature [0007] Patent Literature 1: Japanese Patent Laid-Open Publication No. 170843/1993 Patent Literature 2: Japanese Patent Laid-Open Publication No. 7703/1991 Patent Literature 3: Japanese Patent Laid-Open Publication No. 120021/1996 Patent Literature 4: Japanese Patent Laid-Open Publication No. 163120/2008 Patent Literature 5: Japanese Patent Laid-Open Publication No. 34478/1972 Summary of Invention Technical Problem [0008] It is an object of the present invention to obtain, with a high activity, a propylene-based block copolymer which has high melt viscoelasticity, excellent valance between rigidity and impact resistance and good molding processability and is extremely excellent in its molded product appearance and to provide a composition containing the copolymer and molded products obtained therefrom. Solution to Problem [0009] In order to solve the above problems associated with the prior art, the present inventors have earnestly studied. As a result, the present inventors have found that from a propylene-based block copolymer containing a "propylene polymer of wide molecular weight distribution" (room temperature n-decane-insoluble portion (Dinsol), which has specific properties and comprises a crystalline propylene-based (co)polymer, and a "copolymer rubber of wide molecular weight distribution" (room temperature n-decane-soluble portion {Dsol), which has specific properties and comprises propylene and one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms, a molded product which is extremely excellent in its molded product appearance and has excellent balance between rigidity and impact resistance can be obtained because of wide molecular weight distributions of the Dsol and the Dinsol constituting the copolymer, high stereoregularity of the Dinsol and a high-molecular weight component contained in the Dsol, and they have accomplished the present invention. [0010] That is to say, the propylene-based block copolymer of the present invention comprises 5 to 80% by weight of a room temperature n-decane-soluble portion (Dsol) and 20 to 95% by weight of a room temperature n-decane-insoluble portion (Dinsol) , with the proviso that the total amount of the Dsol and the Dinsol is 100% by weight, and satisfies the following requirements [1] to [3] at the same time: [0011] [1] the molecular weight distribution (Mw/Mn) of the Dsol is not less than 7.0 but not more than 30, [2] the molecular weight distribution (Mw/Mn) of the Dinsol is not less than 7.0 but not more than 30, and Mz/Mw thereof is not less than 6.0 but not more than 20, and [3] the pentad fraction (mmmm) of the Dinsol is not less than 93%. [0012] The propylene-based block copolymer further satisfies, in addition to the above requirements [1] to [3], the following requirements [4] and [5]: [0013] [4] the intrinsic viscosity [n] (dl/g) of the Dsol is not less than 1.5 but not more than 10.0, and [5] Mz/Mn of the Dinsol is not less than 70 but not more than 300. [0014] The room temperature n-decane-soluble portion (Dsol) contains, as a main component, a copolymer rubber comprising propylene and one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms, and the room temperature n-decane-insoluble portion (Dinsol) contains, as amain component, a crystalline propylene-based (co)polymer comprising 98.5 to 100% by mol of propylene and 0 to 1.5% by mol of one or more olefins selected from ethylene and a-olefins of 4 to 20 carbon atoms. [0015] The step for preparing the copolymer rubber comprises polymerizing propylene and one or more olefins selected from ethylene and a-olefins of 4 to 20 carbon atoms in one stage. [0016] The propylene-based block copolymer is obtained by polymerization in the presence of an olefin polymerization catalyst comprising a solid titanium catalyst component (I) containing titanium, magnesium, halogen, a cyclic ester compound (a) represented by the following formula (1) and a cyclic ester compound (b) represented by the following formula (2), an organometallic compound (II) containing a metal atom selected from Group 1, Group 2 and Group 13 of the periodic table, and if necessary, an electron donor (III); [0017] (Formula Removed) [0018] wherein n is an integer of 5 to 10, [0019] R2 and R3 are each independently COOR1 or R, at least one of R2 and R3 is COOR1, and single bonds (C-Cb bond, Ca-Cb bond in the case where R3 is COOR1, and C-C bond (in the case where n is 6 to 10) ) in the cyclic skeleton may be each replaced with a double bond, [0020] each R1 is independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, [0021] plural R are each independently an atom or a group selected from a hydrogen atom, a hydrocarbon group of 1 to 20 carbon atoms, a halogen atom, a nitrogen-containing group, an oxygen-containing group, a phosphorus-containing group, a halogen-containing group and a silicon-containing group, and they may be bonded to one another to form a ring, but at least one R is not a hydrogen atom, [0022] in a skeleton of the ring formed from plural R bonded to one another, a double bond may be contained, and when two or more Ca to each of which COOR1 is bonded are contained in the skeleton of the ring, the number of carbon atoms to constitute the skeleton of the ring is in the range of 5 to 10; [0023] [Chem. 2] (Formula Removed) [0024] wherein n is an integer of 5 to 10, [0025] R4 and R5 are each independently COOR1 or a hydrogen atom, at least one of R4 and R5 is COOR1, each R1 is independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, and single bonds (C-Cb bond, Ca-Cb bond in the case where R5 is COOR1, and C-C bond (in the case where n is 6 to 10) ) in the cyclic skeleton may be each replaced with a double bond. [0026] In the formula (1) and the formula (2), it is preferable that all the bonds between carbon atoms in the cyclic skeletonare singlebonds . Intheformula (1) and the formula (2), it is also preferable that n is 6. [0027] It is preferable that the cyclic ester compound (a) is represented by the following formula (la), and the cyclic ester compound (b) is represented by the following formula (2a) ; [0028] [Chem. 3] (Formula Removed) [0029] wherein n is an integer of 5 to 10, [0030] singlebonds (C-C bond (in the case where n is 6 to 10) , Ca-C bond and Cb-C bond) in the cyclic skeleton may be each replaced with a double bond, [0031] each R1 is independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, [0032] plural R are each independently an atom or a group selected from a hydrogen atom, a hydrocarbon group of 1 to 20 carbon atoms, a halogen atom, a nitrogen-containing group, an oxygen-containing group, a phosphorus-containing group, a halogen-containing group and a silicon-containing group, and they may be bonded to one another to form a ring, but at least one R is not a hydrogen atom, [0033] in a skeleton of the ring formed from plural R bonded to one another, a double bond may be contained, and when two or more Ca to each of which COOR1 is bonded are contained in the skeleton of the ring, the number of carbon atoms to constitute the skeleton of the ring is in the range of 5 to 10; [0034] [Chem. 4] (Formula Removed) [0035] wherein n is an integer of 5 to 10, [0036] each R1 is independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, and single bonds (C-C bond (in the case where n is 6 to 10), Ca-C bond and Cb-C bond) in the cyclic skeleton may be each replaced with a double bond. [0037] In the formula (la) and the formula (2a) , it is preferable that all the bonds between carbon atoms in the cyclic skeleton are single bonds. In the formula (la) and the formula (2a), it is also preferable that n is 6. [0038] The propylene resin composition of the present invention comprises the above-mentioned propylene-based block copolymer, and an inorganic filler and/or an elastomer. [0039] The molded product of the present invention comprises the above-mentioned propylene-based block copolymer. Advantageous Effects of Invention [0040] The propylene-based block copolymer of the present invention can achieve high melt viscoelasticity by virtue of an ultrahigh-molecular weight rubber component contained in a slight amount in the copolymer rubber of wide molecular weight distribution, even if fluidity of the propylene polymer of wide molecular weight distribution is increased. As a result, stabilization of in-mold flow during the injection molding can be achieved, and hence, an effect that flow mark hardly occurs is exerted. At the same time, an effect that the molded product rarely suffers surface appearance defects such as fish eye and graininess is exerted because it is unnecessary to increase a molecular weight of the whole copolymer rubber of wide molecular weight distribution in order to improve occurrence of flow mark. [0041] Moreover, the propylene-based block copolymer of the present invention has, as a constitutional unit, a copolymer rubber of wide-molecular weight distribution containing a high-molecular weight rubber component, and hence, the glass transition temperature is lowered. By virtue of these properties, the propylene-based block copolymer of the present invention has an effect that it exhibits good low-temperature impact resistance. [0042] Furthermore, by virtue of orientation crystallization of the wide-molecular weight distribution propylene polymer having high stereoregularity and wide molecular weight distribution, the propylene-based block copolymer of the present invention has an effect that this copolymer has high rigidity without impairing impact resistance. [0043] In addition, by virtue of orientation crystallization of the propylene polymer having high stereoregularity and wide molecular weight distribution, the propylene-based block copolymer of the present invention has an effect that an injection molded product of this copolymer has a low linear expansion coefficient and has high dimensional accuracy. [004 4] Since the propylene-based block copolymer of the present invention has such effects as above, a composition containing the copolymer and molded products obtained therefrom can be used as materials of various molded articles having excellent properties, particularly large-sized injection molded articles such as automotive interior or exterior trim parts and household appliance parts. Brief Description of Drawings [0045] Fig. 1 is a schematic view of a molded article shape, which is used for visual evaluation of appearance flow mark of an injection molded article. Fig. 2 is a view of a specimen for appearance flow mark test of an injection molded article, said specimen being obtained from a propylene-based block copolymer of Example 1 (appearance flow mark evaluation: 9.5 points). Fig.3 is a view of a specimen for appearance flow mark test of an injection molded article, said specimen being obtained from a propylene-based block copolymer of Comparative Example 2 (appearance flow mark evaluation: 3.0 points). Description of Embodiments [004 6] The propylene-based block copolymer of the present invention, the composition containing the copolymer and the molded products obtained therefrom are described in detail hereinafter. [0047] Propylene-based block copolymer The propylene-based block copolymer of the present invention comprises 5 to 80% by weight, preferably 10 to 50% by weight, more preferably 10 to 30% by weight, of a room temperature n-decane-soluble portion (Dsol) and 20 to 95% by weight, preferably 50 to 90% by weight, more preferably 70 to 90% by weight, of a room temperature n-decane-insoluble portion (Dinsol), with the proviso that the total amount of the Dsol and the Dinsol is 100% by weight. [0048] The room temperature n-decane-soluble portion (Dsol) contains, as a main component (larger than 50% by weight, preferably 80 to 100% by weight, more preferably 90 to 100% by weight), a propylene-based copolymer rubber comprising propylene and one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms. The content of one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms in the propylene-based copolymer rubber is higher than the content of the olefins in the later-described propylene-based polymer. [0049] The room temperature n-decane-insoluble portion (Dinsol) contains, as a main component (larger than 50% by weight, preferably 80 to 100% by weight, more preferably 90 to 100% by weight), a crystalline propylene-based (co)polymer. The crystalline propylene-based (co)polymer is a crystalline propylene homopolymer or a crystalline propylene-based copolymer containing propylene and not more than 1.5% by mol of one or more olefins selected from ethylene and a-olefins of 4 to 20 carbon atoms. [0050] The propylene-based block copolymer of the present invention satisfies the later-described requirements [1] to [3] at the same time, and preferably further satisfies the requirement [4] and/or the requirement [5] at the same time. In the present invention, the "room temperature n-decane-soluble portion (Dsol)" indicates a portion in the propylene-based block copolymer, which is being dissolved in n-decane after the copolymer is heated at 150°C for 2 hours in n-decane to dissolve it and then cooled down to 23°C, as described in detail in the examples given later. In the following description, the "room temperature n-decane-soluble portion" and the "room temperature n-decane-insoluble portion" are sometimes called "n-decane-soluble portion" and "n-decane-insoluble portion" for short, respectively. [0051] The propylene-based block copolymer of the present invention is constituted of a skeleton (as a main skeleton) attributable to propylene and a skeleton attributable to one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms. Examples of the a-olefins of 4 to 20 carbon atoms include 1-butene, 1-pentene, l~hexene, 4-methyl-l-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. As the olefin to constitute the skeleton attributable to one or more olefins selected from ethylene and a-olefins of 4 to 20 carbon atoms in the copolymer, preferable is ethylene or an α-olefin of 4 to 10 carbon atoms, and more preferable is ethylene, 1-butene, 1-pentene, 1-hexcene, 4-methyl-l-pentene, 1-octene or 1-decene. It is still more preferable to use one or more kinds of these olefins. [0052] The requirements [1] to [3] which the propylene-based block copolymer of the present invention should satisfy and the requirements [4] and [5] which the copolymer satisfies when needed are as follows. [0053] [1] The molecular weight distribution (Mw/Mn) of the Dsol is not less than 7.0 but not more than 30. [0054] [2] The molecular weight distribution (Mw/Mn) of the Dinsol is not less than 7.0 but not more than 30, and Mz/Mw thereof is not less than 6.0 but not more than 20. [0055] [3] The pentad fraction (mmmm) of the Dinsol is not less than 93%. [0056] [4] The intrinsic viscosity [n] (dl/g) of the Dsol is not less than 1.5 but not more than 10.0. [0057] [5] Mz/Mn of the Dinsol is not less than 70 but not more than 300. [0058] The requirements [1] to [5] of the propylene-based block copolymer of the present invention are described below in detail. [0059] Requirement [1] The Mw/Mn value of the decane-soluble portion (Dsol) in the propylene-based block copolymer of the present invention, which is a ratio of a weight-average molecular weight (Mw) to a number-average molecular weight (Mn) and determined from measured values given by gel permeation chromatography (GPC), is in the range of 6.0 to 30, and from the viewpoint of compatibility of high fluidity with high melt tension, it is preferably in the range of 6.5 to 20, more preferably 7.0 to 18. [0060] Since the Mw/Mn of the decane-soluble portion (Dsol) in the propylene-basedblockcopolymer of the present invention is high, this copolymer is characterized by containing a large amount of a high-molecular weight copolymer rubber component. Owing to such a characteristic, melt elasticity of the propylene-based block copolymer of the present invention can be increased by the high-molecular weight copolymer rubber component even if MFR of the propylene-based polymer of wide-molecular weight distribution is high. Therefore, such a high Mw/Mn value is advantageous in attaining compatibility of high fluidity with high melt tension. [0061] When the fluidity of the propylene-based block copolymer is high, injection molding to produce large-sized products and shortening of injection molding cycle are possible. When the melt elasticity of the propylene-based block copolymer is high, appearance of injection molded articles becomes good, and blow molding properties or foam molding properties become good, that is, impartation of molding processability to the copolymer becomes possible. [0062] The requirement [1] can be attained by copolymerizing propylene and one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms in the presence of the later-described olefin polymerization catalyst. [0063] The requirement [1] can be attained by carrying out the polymerization in plural stages even if an olefin polymerization catalyst already known is used, but in the present invention, by the use of the later-described olefin polymerization catalyst, it becomes possible to obtain a copolymer satisfying the desired requirement even in the polymerization of one stage. By virtue of this, there is an advantage that the resulting copolymer rubber component is not aggregated and is apt to be more finely dispersed in the propylene-based block copolymer. Moreover, a simpler polymer production apparatus can be used, and this is advantageous from the viewpoints of economy and energy saving. The "polymerization of one stage" used herein means that the step for producing the copolymer rubber is made up by a stage of one reactor and the polymerization conditions in the reactor are not changed at all. [0064] Requirement [2] The Mw/Mn value of the decane-insoluble portion (Dinsol) in the propylene-based block copolymer of the present invention, as determined from measured values given by gel permeation chromatography (GPC) , is in the range of 7.0 to 30, and from the viewpoint of retention of high rigidity and impact resistance, the Mw/Mn value is preferably in the range of 7.0 to 20, more preferably 8.0 to 18. [0065] The Mz/Mw value of the decane-insoluble portion (Dinsol) in the propylene-based block copolymer of the present invention, as determined from measured values given by gel permeation chromatography (GPC), is in the range of 6 to 20, preferably 6.5 to 18, more preferably 7 to 15. [0066] Since the decane-insoluble portion (Dinsol) in the propylene-based block copolymer of the present invention has a high Mw/Mn value, the copolymer exhibits a sufficiently wide molecular weight distribution and is excellent not only in moldability but also in rigidity. Further, since the decane-insoluble portion has a high Mz/Mw value as described above, the propylene-based block copolymer of the present invention contains a large amount of a high-molecular weight component, so that the propylene-based block copolymer has high melt tension (MT) and excellent moldability. [0067] Such a decane-insoluble portion (Dinsol) in the propylene-based block copolymer of the present invention as above can be prepared by polymerization of plural stages or mixing of plural kinds of polypropylenes, but it is preferable to obtain it by polymerization of one stage. When the decane-insoluble portion (Dinsol) of the propylene-based block copolymer of the present invention is obtained by polymerization of one stage, a simpler polymer production apparatus can be used, and this is economical. Moreover, the high-molecular weight component is not aggregated and is more finely dispersed in the propylene-based block copolymer, so that polymerization of one stage is preferable. [0068] The decane-insoluble portion (Dinsol) in the propylene-based block copolymer of the present invention has a high Mw/Mn value and contains a large amount of a high-molecular weight component having a high Mz/Mw value and preferably further having a high Mz/Mn value that is described later. Therefore, the high-molecular weight component in the propylene-based block copolymer functions as a nucleating agent in the molding process, and even if a nucleating agent such as a filler powder or a resin powder is not added, a molded product having a high crystallinity can be sometimes obtained. Especially when the high-molecular weight component is finely dispersed, the function of the nucleating agent tends to be enhanced, so that such a case is preferable. [0069] The requirement [2] can be attained by polymerizing 98.5 to 100% by mol of propylene and 0 to 1.5% by mol of one or more olefins selected from ethylene and α-olefins of 4 to 20 carbon atoms in the presence of the later-described olefin polymerization catalyst. [0070] Requirement [3] The pentad fraction (mmmm) of the decane-insoluble portion (Dinsol) in the propylene-based block copolymer of the present invention is not less than 93%, preferably not less than 94%, more preferably not less than 95% . The upper limit of the pentad fraction is 100%, preferably 99.8%, more preferably 99.5%. A pentad fraction (mmmm) of less than 93% is undesirable because rigidity is lowered, or in some fields of products such as films, heat resistance required cannot be occasionally secured. [0071] For example, in a propylene-based polymer produced by the use of a titanium trichloride catalyst, the decane-insoluble portion has an extremely low pentad fraction of about 91 to 92% though an effect attributable to widening of a molecular weight distribution is exerted, as described in the aforesaidpatent literature 5, and therefore, such a polymer cannot be used for injection molded products requiring high rigidity, such as automotive materials. [0072] That the requirement [3] is satisfied is attributable to the fact that a cyclic ester compound (a) and a cyclic ester compound (b) are contained as electron donors in the later-described olefin polymerization catalyst. [0073] Requirement [4] The intrinsic viscosity [n] (dl/g) of the decane-soluble portion (Dsol) in thepropylene-basedblockcopolymer of the present invention is usually in the range of 1.5 to 10.0, and from the viewpoint of optimization of a balance among impact resistance, high fluidity and high melt elasticity, it is preferably in the range of 2.0 to 7.0, more preferably 2.5 to 4.0. An intrinsic viscosity [n] (dl/g) of less than 1.5 dl/g is undesirable because impact resistance of the propylene-based block copolymer is liable to be lowered. If the intrinsic viscosity [n] (dl/g) is higher than 10 dl/g, fluidity is liable to be lowered or fish eye is apt to occur, and hence, application to large-sized injected molded articles or films sometimes becomes difficult. [0074] It has been considered to be a matter of common knowledge by a person skilled in the art that the effects such as impact resistance, high fluidity and high melt elasticity can be exerted by post addition of a propylene-based copolymer rubber having a high intrinsic viscosity [n] (dl/g) of the decane-soluble portion (Dsol). In this case, however, there is a problem that fish eye is apt to occur, and from the viewpoint of deterioration of molded article appearance, industrialization is difficult. On the other hand, in the case of a propylene-based block copolymer obtained by continuously polymerizing the decane-soluble portion (Dsol) as in the present invention, the copolymer rubber is finely dispersed in the whole copolymer. Therefore, such a defect as above does not occur, and in addition to the above effects such as impact resistance, high fluidity and high melt elasticity of the copolymer, molded articles inhibited from occurrence of fish eye can be obtained. [0075] Requirement [5] The Mz/Mn value of the decane-insoluble portion (Dinsol) in the polypropylene-based block copolymer of the present invention is in the range of 70 to 300, preferably 100 to 250, more preferably 120 to 200. [0076] Polypropylene having a high Mz/Mn value indicates that the content of the high-molecular weight component is high, and the polypropylene is expected to have high possibilities of high melt tension and excellent moldability and rigidity. [0077] A propylene-based polymer produced by the use of, for example, a titanium trichloride catalyst has an effect attributable to widening of a molecular weight distribution, as described in the aforesaid patent literature 5, but the widening of a molecular weight distribution greatly depends upon increase of a low-molecular weight polymer, so that the Mz/Mn value of the propylene-based polymer produced by the use of a titanium trichloride catalyst is at most about 40. Accordingly, the propylene-based polymer is unsuitable for injection molded products such as automotive materials, which require an effect attributable to a large amount of a high-molecular weight polymer as in the present invention, namely, high rigidity. [0078] The propylene-based block copolymer satisfying the above requirements [1] to [3] at the same time, more preferably further satisfying the requirements [4] and [5], is preferably prepared by the use of the following olefin polymerization catalyst. [0079] Olefin polymerization catalyst The propylene-based block copolymer of the present invention is preferably obtained by polymerization in the presence of an olefin polymerization catalyst comprising a solid titanium catalyst component (I), an organometallic compound (II) containing a metal atom selected from Group 1, Group 2 and Group 13 of the periodic table, and if necessary, an electron donor (III) . The components of the olefin polymerization catalyst are described below in detail. [0080] Solid titanium catalyst component (I) The solid titanium catalyst component (I) for the present invention contains titanium, magnesium, halogen, a cyclic ester compound (a) represented by the following formula (1) and a cyclic ester compound (b) represented by the following formula (2). [0081] Cyclic ester compound (a) The cyclic ester compound (a) has plural carboxylic acid ester groups and is represented by the following formula (1). [0082] [Chem. 5] (Formula Removed) [0083] In the formula (1) , n is an integer of 5 to 10, preferably an integer of 5 to 7, particularly preferably 6. Ca and Cb are each a carbon atom. [0084] R2 and R3 are each independently COOR1 or R, and at least one of R2 and R3 is COOR1. [0085] All the bonds between carbon atoms in the cyclic skeleton are preferably single bonds, but any of single bonds in the cyclic skeleton, other than Ca-Ca bond and Ca-Cb bond in the case where R3 is R, may be replaced with a double bond. That is to say, C-Cb bond, Ca-Cb bond in the case where R3 is COOR1, and C-C bond (in the case where n is 6 to 10) in the cyclic skeleton may be each replaced with a double bond. [0086] Plural R1 are each independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, still more preferably 4 to 8 carbon atoms, particularly preferably 4 to 6 carbon atoms. Examples of the hydrocarbon groups include methyl group, ethyl group, n-propylgroup, isopropylgroup, n-butyl group, isobutyl group, hexyl group, heptyl group, octyl group, 2-ethylhexyl group, decyl group, dodecyl group, tetradecyl group, hexadecyl group, octadecyl group and eicosyl group. Of these, n-butyl group, isobutyl group, hexyl group and octyl group are preferable, and n-butyl group and isobutyl group are particularly preferable because a propylene-based block copolymer having a wide molecular weight distribution can be prepared. [0087] Plural R are each independently an atom or a group selected from a hydrogen atom, a hydrocarbon group of 1 to 20 carbon atoms, a halogen atom, a nitrogen-containing group, an oxygen-containing group, a phosphorus-containing group, a halogen-containing group and a silicon-containing group, but at least one R is not a hydrogen atom. [0088] R other than a hydrogen atom is preferably a hydrocarbon group of 1 to 20 carbon atoms among them, and examples of the hydrocarbon groups of 1 to 20 carbon atoms include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups and aromatic hydrocarbon groups, such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, n-pentyl group, cyclopentyl group, n-hexyl group, cyclohexyl group, vinyl group, phenyl group and octyl group. Of these, aliphatic hydrocarbon groups are preferable, and specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group and sec-butyl group are preferable. [0089] Moreover, plural R may be bonded to one another to form a ring, and in the skeleton of the ring formed from plural R bonded to one another, a double bond may be contained. When two or more Ca to each of which COOR1 is bonded are contained in the skeleton of the ring, the number of carbon atoms to constitute the skeleton of the ring is in the range of 5 to 10. [0090] Examples of such skeletons of the rings include norbornane skeleton and tetracyclododecene skeleton. [0091] Furthermore, plural R may be each a carbonyl structure-containing group, such as carbonic acid ester group, alkoxy group, siloxy group, aldehyde group or acetyl group, and in these substituents, one or more hydrocarbon groups of 1 to 20 carbon atoms are preferably contained. [0092] Such a cyclic ester compound (a) is described in International Publication No. 2006/077945 pamphlet. Examples of such compounds include: diethyl 3-methylcyclohexane-l,2-dicarboxylate, di-n-propyl 3-methylcyclohexane-l,2-dicarboxylate, diisopropyl 3-methylcyclohexane-l,2-dicarboxylate, di-n-butyl 3-methylcyclohexane-l,2-dicarboxylate, diisobutyl 3-methylcyclohexane-l,2-dicarboxylate, dihexyl 3-methylcyclohexane-l,2-dicarboxylate, diheptyl 3-methylcyclohexane-l,2-dicarboxylate, dioctyl 3-methylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 3-methylcyclohexane-l,2-dicarboxylate, didecyl 3-methylcyclohexane-l,2-dicarboxylate, diethyl 4-methylcyclohexane-l,3-dicarboxylate, diisobutyl 4-methylcyclohexane-l,3-dicarboxylate, diethyl 4-methylcyclohexane-l,2-dicarboxylate, di-n-propyl 4-methylcyclohexane-l,2-dicarboxylate, diisopropyl 4-methylcyclohexane-l,2-dicarboxylate, di-n-butyl 4-methylcyclohexane-l,2-dicarboxylate, diisobutyl 4-methylcyclohexane-l,2-dicarboxylate, dihexyl 4-methylcyclohexane-l,2-dicarboxylate, diheptyl 4-methylcyclohexane-l,2-dicarboxylate, dioctyl 4-methylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 4-methylcyclohexane-l,2-dicarboxylate, didecyl 4-methylcyclohexane-l,2-dicarboxylate, diethyl 5-methylcyclohexane-l, 3-dicarboxylate, diisobutyl 5-methylcyclohexane-l,3-dicarboxylate, diethyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, di-n-propyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, diisopropyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, di-n-butyl 3,4-dimethylcyclohexane-l, 2-dicarboxylate, diisobutyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, dihexyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, diheptyl 3, 4-dimethylcyclohexane-l, 2-dicarboxylate, dioctyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, didecyl 3,4-dimethylcyclohexane-l,2-dicarboxylate, diethyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-n-propyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, diisopropyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-n-butyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, diisobutyl 3,6-dimethylcyclohexane-l, 2-dicarboxylate, dihexyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, diheptyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, dioctyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, didecyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, diethyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, di-n-propyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, diisopropyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, di-n-butyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, diisobutyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, dihexyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, dioctyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, didecyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, diethyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-n-propyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diisopropyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-n-butyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diisobutyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, dihexyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diheptyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, dioctyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, didecyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diethyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-n-propyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diisopropyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-n-butyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diisobutyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, dihexyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, diheptyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, dioctyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, didecyl 3-methyl-6~ethylcyclohexane-l,2-dicarboxylate, diethyl 3-methyl-6-n-propylcyclohexane-l, 2-dicarboxylate, di-n-propyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, diisopropyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, di-n-butyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, diisobutyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, dihexyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, diheptyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, dioctyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, di-2-ethylhexyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, didecyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, diethyl 3-hexylcyclohexane-l, 2-dicarboxylate, diisobutyl 3-hexylcyclohexane-l,2-dicarboxylate, diethyl 3,6-dihexylcyclohexane-l,2-dicarboxylate, diisobutyl 3-hexyl-6-pentylcyclohexane-l,2-dicarboxylate, diethyl 3-methylcyclopentane-l,2-dicarboxylate, diisobutyl 3-methylcyclopentane-l,2-dicarboxylate, diheptyl 3-methylcyclopentane-l,2-dicarboxylate, didecyl 3-methylcyclopentane-l,2-dicarboxylate, diethyl 4-methylcyclopentane-l,3-dicarboxylate, diisobutyl 4-methylcyclopentane-l,3-dicarboxylate, diethyl 4-methylcyclopentane-l,2-dicarboxylate, diisobutyl 4-methylcyclopentane-l,2-dicarboxylate, diheptyl 4-methylcyclopentane-l,2-dicarboxylate, didecyl 4-methylcyclopentane-l,2-dicarboxylate, diethyl 5-methylcyclopentane-l,3-dicarboxylate, diisobutyl 5-methylcyclopentane-l,3-dicarboxylate, diethyl 3,4-dimethylcyclopentane-l,2-dicarboxylate, diisobutyl 3,4-dimethylcyclopentane-l,2-dicarboxylate, diheptyl 3,4-dimethylcyclopentane-l,2-dicarboxylate, didecyl 3,4-dimethylcyclopentane-l,2-dicarboxylate, diethyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, diisobutyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, diheptyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, didecyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, diethyl 3-hexylcyclopentane-l,2-dicarboxylate, diethyl 3,5-dihexylcyclopentane-l,2-dicarboxylate, diisobutyl 3-hexyl-5-pentylcyclopentane-l,2-dicarboxylate, diethyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, di-n-propyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, diisopropyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, di-n-butyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, diisobutyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, dihexyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, dioctyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, didecyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, diethyl 3-methylcycloheptane-l,2-dicarboxylate, diisobutyl 3-methylcycloheptane-l,2-dicarboxylate, diheptyl 3-methylcycloheptane-l,2-dicarboxylate, didecyl 3-methylcycloheptane-l,2-dicarboxylate, diethyl 4-methylcycloheptane-l,3-dicarboxylate, diisobutyl 4-methylcycloheptane-l,3-dicarboxylate, diethyl 4-methylcycloheptane-l,2-dicarboxylate, diisobutyl 4-methylcycloheptane-l,2-dicarboxylate, diheptyl 4-methylcycloheptane-l,2-dicarboxylate, didecyl 4-methylcycloheptane-l,2-dicarboxylate, diethyl 5-methylcycloheptane-l,3-dicarboxylate, diisobutyl 5-methylcycloheptane-l,3-dicarboxylate, diethyl 3,4-dimethylcycloheptane-l,2-dicarboxylate, diisobutyl 3,4-dimethylcycloheptane-l,2-dicarboxylate, diheptyl 3,4-dimethylcycloheptane-l,2-dicarboxylate, didecyl 3,4-dimethylcycloheptane-l,2-dicarboxylate, diethyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, diisobutyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, diheptyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, didecyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, diethyl 3-hexylcycloheptane-l,2-dicarboxylate, diethyl 3,7-dihexylcycloheptane-l,2-dicarboxylate, diisobutyl 3-hexyl-7-pentylcycloheptane-l,2-dicarboxylate, diethyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, di-n-propyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, diisopropyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, di-n-butyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, diisobutyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, dihexyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, dioctyl 3-methyl-7-n-propylcycloheptane~l,2-dicarboxylate, didecyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, diethyl 3-methylcyclooctane-l,2-dicarboxylate, diethyl 3-methylcyclodecane-l,2-dicarboxylate, diisobutyl 3-vinylcyclohexane-l,2-dicarboxylate, diisobutyl 3,6-diphenylcyclohexane-l,2-dicarboxylate, diethyl 3,6-dicyclohexylcyclohexane-l,2-dicarboxylate, diisobutyl norbornane-2,3-dicarboxylate, diisobutyl tetracyclododecane-2,3-dicarboxylate, diethyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, di-n-propyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, diisopropyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, di-n-butyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, diisobutyl 3,6-dimethyl-4-cyclohexene-l, 2-dicarboxylate, dihexyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, diheptyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, dioctyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, di-2-ethylhexyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, didecyl 3,6-dimethyl-4-cyclohexene-l,2-dicarboxylate, diethyl 3, 6-dihexyl-4-cyclohexene-l,2-dicarboxylate, and diisobutyl 3-hexyl-6-pentyl-4-cyclohexene-l,2-dicarboxylate. 10093] As preferred examples, there can be also mentioned the following compounds: 3,6-dimethylcyclohexane-l,2-diacetate, 3,6-dimethylcyclohexane-l,2-dibutanate, 3-methyl-6-propylcyclohexane-l,2-diol acetate, 3-methyl-6-propylcyclohexane-l,2-butanate, 3,6-dimethylcylohexane-l,2-dibenzoate, 3,6-dimethylcyclohexane-l,2-ditoluate, 3-methyl-6-propylcyclohexane-l,2-dibenzoate, 3-methyl-6-propylcyclohexane-l,2-ditoluate, etc. [0094] In such compounds having a diester structure as above, isomers such as cis and trans isomers derived from plural COOR1 groups in the formula (1) are present, and any structure of the isomers has an effect which agrees with the object of the present invention, but a higher content of the trans isomer is preferable. When the content of the trans isomer is higher, not only an effect of widening a molecular weight distribution is exerted but also activity and stereoregularity of the resulting polymer tend to become higher. [0095] As the cyclic ester compounds (a), compounds represented by the following formulas (1-1) to (1-6) are preferable. [0096] [Chem. 6] [0097] [Chem. 7] [0098] [Chem. 8] [0099] [Chem. 9] [0100] [Chem. 10] [0101] [Chem. 11] (Formula Removed) [0102] Definitions of R1 and R in the formulas (1-1) to (1-6) are the same as those in the formula (1). [0103] In the formulas (1-1) to (1-3), single bonds in the cyclic skeleton (excluding Ca-Ca bond and Ca-Cb bond) may be each replaced with a double bond. [0104] In the formulas (1-4) to (1-6), single bonds in the cyclic skeleton (excluding Ca-Ca bond) may be each replaced with a double bond. [0105] In the formulas (1-3) and (1-6), n is an integer of 7 to 10. As the cyclic ester compound (a), a compound represented by the following formula (la) is particularly preferable. [0106] [Chem. 12] (Formula Removed) [0107] Definitions of n, R1 and R in the formula (la) are the same as those in the formula (1), and single bonds in the cyclic skeleton (excluding Ca-Ca bond and Ca-Cb bond) may be each replaced with a double bond. That is to say, C-C bond (in the case where n is 6 to 10), Ca-C bond and Cb-C bond in the cyclic skeleton may be each replaced with a double bond. Examples of the compounds represented by the formula (la) include: diisobutyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-n-octyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, diisobutyl 3-methyl-6-ethylcyclohexane-l, 2-dicarboxylate, di-n-hexyl 3-methyl-6-ethylcyclohexane-l, 2-dicarboxylate, di-n-octyl 3-methyl-6-ethylcyclohexane-l, 2-dicarboxylate, diisobutyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, di-n-octyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, diisobutyl 3,6-diethylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3,6-diethylcyclohexane-l,2-dicarboxylate, di-n-octyl 3,6-diethylcyclohexane-l,2-dicarboxylate, diisobutyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, di-n-hexyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, di-n-octyl 3,5-dimethylcyclopentane-l,2-dicarboxylate, diisobutyl 3-methyl-5-ethylcyclopentane-l,2-dicarboxylate, di-n-hexyl 3-methyl-5-ethylcyclopentane-l,2-dicarboxylate, di-n-octyl 3-methyl-5-ethylcyclopentane-l, 2-dicarboxylate, di-n-hexyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, di-n-octyl 3-methyl-5-n-propylcyclopentane-l,2-dicarboxylate, diisobutyl 3,5-diethylcyclopentane-l,2-dicarboxylate, di-n-hexyl 3,5-diethylcyclopentane-l,2-dicarboxylate, di-n-octyl 3,5-diethylcyclopentane-l,2-dicarboxylate, diisobutyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, di-n-hexyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, di-n-octyl 3,7-dimethylcycloheptane-l,2-dicarboxylate, diisobutyl 3-methyl-7-ethylcycloheptane-l,2-dicarboxylate, di-n-hexyl 3-methyl-7-ethylcycloheptane-l,2-dicarboxylate, di-n-octyl 3-methyl-7-ethylcycloheptane-l,2-dicarboxylate, di-n-hexyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, di-n-octyl 3-methyl-7-n-propylcycloheptane-l,2-dicarboxylate, diisobutyl 3,7-diethylcycloheptane-l,2-dicarboxylate, di-n-hexyl3,7-diethylcycloheptane-l,2-dicarboxylate,and di-n-octyl 3,7-diethylcycloheptane-l,2-dicarboxylate. [0108] Of the above compounds, more preferable are: diisobutyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, di-n-octyl 3,6-dimethylcyclohexane-l,2-dicarboxylate, diisobutyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3-methyl-6-ethylcyclohexane-l,2-dicarboxylate, di-n-octyl 3-methyl-6-ethylcyclohexane-l, 2-dicarboxylate, diisobutyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3-methyl-6-n-propylcyclohexane-l, 2-dicarboxylate, di-n-octyl 3-methyl-6-n-propylcyclohexane-l,2-dicarboxylate, diisobutyl 3,6-diethylcyclohexane-l,2-dicarboxylate, di-n-hexyl 3,6-diethylcyclohexane-l,2-dicarboxylate, and di-n-octyl 3,6-diethylcyclohexane-l,2-dicarboxylate. These compounds can be prepared by utilizing the Diels-Alder reaction. [0109] In such cyclic ester compounds (a) having a diester structure as above, isomers such as cis and trans isomers are present, and any structure of the isomers has an effect which agrees with the object of the present invention, but a higher content of the trans isomer is particularly preferable because not only an effect of widening a molecular weight distribution is exerted but also activity and stereoregularity of the resulting polymer tend to become higher. In the cis and trans isomers, the proportion of the trans isomer is preferably not less than 51%. The lower limit is more preferably 55%, still more preferably 60%, particularly preferably 65%. On the other hand, the upper limit is preferably 100%, more preferably 90%, still more preferably 85%, particularly preferably 79%. [0110] Cyclic ester compound (b) The cyclic ester compound (b) has plural carboxylic acid ester groups and is represented by the following formula (2). [0111] [Chem. 13] (Formula Removed) [0112] In the formula (2), n is an integer of 5 to 10, preferably an integer of 5 to 7, particularly preferably 6. Ca and Cb are each a carbon atom. [0113] All the bonds between carbon atoms in the cyclic skeleton are preferably single bonds, but any of single bonds in the cyclic skeleton, other than Ca-Ca bond and Ca-Cb bond in the case where R5 is a hydrogen atom, may be replaced with a double bond. That is to say, Ca-Ca bond, Ca-Cb bond in the case where R5 is COOR1 and C-C bond (in the case where n is 6 to 10) in the cyclic skeleton may be each replaced with a double bond. [0114] R4 and R5 are each independently COOR1 or a hydrogen atom, at least one of R4 and R5 is COOR1, and each R1 is independently a monovalent hydrocarbon group of 1 to 20 carbon atoms. [0115] Plural R1 are each independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, still more preferably 4 to 8 carbon atoms, particularly preferably 4 to 6 carbon atoms. Examples of the hydrocarbon groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, hexyl group, heptyl group, octyl group, 2-ethylhexyl group, decyl group, dodecyl group, tetradecyl group, hexadecyl group, octadecyl group and eicosyl group. Of these, n-butyl group, isobutyl group, hexyl group and octyl group are preferable, and n-butyl group and isobutyl group are particularly preferable because a propylene-based block copolymer having a wide molecular weight distribution can be prepared. [0116] Examples of such cyclic ester compounds (b) include: diethyl cyclohexane-1,2-dicarboxylate, di-n-propyl cyclohexane-1,2-dicarboxylate, diisopropyl cyclohexane-1,2-dicarboxylate, di-n-butyl cyclohexane-1,2-dicarboxylate, diisobutyl cyclohexane-1,2-dicarboxylate, dihexyl cyclohexane-1,2-dicarboxylate, diheptyl cyclohexane-1,2-dicarboxylate, dioctyl cyclohexane-1,2-dicarboxylate, di-2-ethylhexyl cyclohexane-1,2-dicarboxylate, didecyl cyclohexane-1,2-dicarboxylate, diethyl cyclohexane-1,3-dicarboxylate, diisobutyl cyclohexane-1,3-dicarboxylate, diethyl cyclopentane-1,2-dicarboxylate, diisopropyl cyclopentane-1,2-dicarboxylate, diisobutyl cyclopentane-1,2-dicarboxylate, diheptyl cyclopentane-1,2-dicarboxylate, didecyl cyclopentane-1,2-dicarboxylate, diethyl cyclopentane-1,3-dicarboxylate, diisobutyl cyclopentane-1,3-dicarboxylate, diethyl cycloheptane-1,2-dicarboxylate, diisopropyl cycloheptane-1,2-dicarboxylate, diisobutyl cycloheptane-1,2-dicarboxylate, diheptyl cycloheptane-1,2-dicarboxylate, didecyl cycloheptane-1,2-dicarboxylate, diethyl cycloheptane-1,3-dicarboxylate, diisobutyl cycloheptane-1,3-dicarboxylate, diethyl cyclooctane-1,2-dicarboxylate, diethyl cyclodecane-1,2-dicarboxylate, diethyl 4-cyclohexene-l,2-dicarboxylate, di-n-propyl 4-cyclohexene-l,2-dicarboxylate, diisopropyl 4-cyclohexene-l,2-dicarboxylate, di-n-butyl 4-cyclohexene-l,2-dicarboxylate, diisobutyl 4-cyclohexene-l,2-dicarboxylate, dihexyl 4-cyclohexene-l,2-dicarboxylate, diheptyl 4-cyclohexene-l,2-dicarboxylate, dioctyl 4-cyclohexene-l,2-dicarboxylate, didecyl 4-cyclohexene-l,2-dicarboxylate, diethyl 4-cyclohexene-l,3-dicarboxylate, diisobutyl 4-cyclohexene-l,3-dicarboxylate, diethyl 3-cyclopentene-l,2-dicarboxylate, diisopropyl 3-cyclopentene-l,2-dicarboxylate, diisobutyl 3-cyclopentene-l,2-dicarboxylate, diheptyl 3-cyclopentene-l,2-dicarboxylate, didecyl 3-cyclopentene-l,2-dicarboxylate, diethyl 3-cyclopentene-l,3-dicarboxylate, diisobutyl 3-cyclopentene-l,3-dicarboxylate, diethyl 4-cycloheptene-l,2-dicarboxylate, diisopropyl 4-cycloheptene-l,2-dicarboxylate, diisobutyl 4-cycloheptene-l,2-dicarboxylate, diheptyl 4-cycloheptene-l,2-dicarboxylate, didecyl 4-cycloheptene-l,2-dicarboxylate, diethyl 4-cycloheptene-l,3-dicarboxylate, diisobutyl 4-cycloheptene-l,3-dicarboxylate, diethyl 5-cyclooctene-l,2-dicarboxylate, and diethyl 6-cyclodecene-l,2-dicarboxylate. [0117] As preferred examples, there can be also mentioned the following compounds: cyclohexane-1,2-diacetate, cyclohexane-1,2-dibutanate, cyclohexane-1,2-dibenzoate, cyclohexane-1,2-ditoluate, etc, [0118] In such cyclic ester compounds having a diester structure as above, isomers such as cis and trans isomers are present, and any structure of the isomers has an effect which agrees with the object of the present invention. In the cis and trans isomers, the proportion of the trans isomer is preferably not less than 51%. The lower limit is more preferably 55%, still more preferably 60%, particularly preferably 65%. On the other hand, the upper limit is preferably 100%, more preferably 90%, still more preferably 85%, particularly preferably 79% . Although the reason is not clear, it is presumed that the variations of the later-described steric isomers are in the region suitable for widening a molecular weight distribution. [0119] In particular, the trans isomer purity of a cyclohexane-1,2-dicarboxylic acid diester wherein n in the formula (2) is 6 is in the above range. [0120] If the trans isomer purity is less than 51%, the effect of widening a molecular weight distribution, activity, stereospecificity, etc. sometimes become insufficient. If the trans isomer purity exceeds 79%, the effect of widening a molecular weight distribution sometimes becomes insufficient. That is to say, a trans isomer purity of the above range is frequently advantageous in achieving compatibility of the effect of widening a molecular weight distribution of the resulting polymer with the activity of the catalyst and the high stereoregularity of the resulting polymer at a high level. [0121] As the cyclic ester compound (b), a compound having a cycloalkane-1,2-dicarboxylic acid diester structure or a cycloalkene-1,2-dicarboxylic acid diester structure, each structure being represented by the following formula (2a), is particularly preferable. [0122] [Chem. 14] (Formula Removed) [0123] In the formula (2a) , n and R1 are the same as above (that is, they have the same definitions as in the formula (2)), and single bonds in the cyclic skeleton (single bonds excluding Ca-Ca bond and Ca-Cb bond, that is, C-Ca bond, C-Cb bond and C-C bond (in the case where n is 6 to 10) ) may be each replaced with a double bond. Examples of the compounds represented by the formula (2a) include: di-n-butyl cyclohexane-1,2-dicarboxylate, diisobutyl cyclohexane-1,2-dicarboxylate, dihexyl cyclohexane-1,2-dicarboxylate, diheptyl cyclohexane-1,2-dicarboxylate, dioctyl cyclohexane-1,2-dicarboxylate, di-2-ethylhexyl cyclohexane-1,2-dicarboxylate, diisobutyl cyclopentane-1,2-dicarboxylate, diheptyl cyclopentane-1,2-dicarboxylate, diisobutyl cycloheptane-1,2-dicarboxylate, and diheptyl cycloheptane-1,2-dicarboxylate. [0124] Of the above compounds, more preferable are: diisobutyl cyclohexane-1,2-dicarboxylate, dihexyl cyclohexane-1,2-dicarboxylate, diheptyl cyclohexane-1,2-dicarboxylate, dioctyl cyclohexane-1,2-dicarboxylate, and di-2-ethylhexyl cyclohexane-1,2-dicarboxylate. The reason is that these compounds not only exhibit catalytic performance but also can be prepared relatively inexpensively utilizing the Diels-Alder reaction. [0125] The cyclic ester compounds (a) and the cyclic ester compounds (b) may be individually used singly or in combination of two or more kinds. [0126] The combined molar ratio between the cyclic ester compound (a) and the cyclic ester compound (b), that is, cyclic ester compound (a)/(cyclic ester compound (a)+cyclic ester compound (b))xi00 (% by mol), is preferably not less than 10% by mol, more preferably not less than 30% by mol, still more preferably not less than 40% by mol, particularly preferably 50% by mol. The upper limit is preferably 99% by mol, more preferably 90% by mol, still more preferably 85% by mol, particularly preferably 80% by mol. [0127] The solid titanium catalyst component (I) of the present invention can provide an olefin polymer having an extremely wide molecular weight distribution under the conditions of a combined molar ratio of the cyclic ester compound (a) in a wide range, that is, even if the content of the cyclic ester compound (a) in the solid titanium catalyst component (I) is low. Although the reason of this effect is not clear, the present inventors have presumed as follows. [0128] It is obvious that the cyclic ester compound (a) has an extremely large number of variations of steric structures which can be formed, because of presence of the substituent R, as compared with the cyclic ester compound (b). On this account, it is thought that the influence of the cyclic ester compound (a) on the molecular weight distribution becomes dominant, and even if the combined molar ratio is low, an olefin polymer having an extremely wide molecular weight distribution can be obtained. [0129] On the other hand, the cyclic ester compound (a) and the cyclic ester compound (b) are relatively similar in the structure, and therefore, with regard to the basic properties such as activity and stereoregulartiy, these compounds hardly have influence on their mutual effects (when compounds having different structures are used, there are many cases where activity, stereoregularity or the like violently changes or the effect of one compound becomes dominant). [0130] On this account, the solid titanium catalyst component (I) for use in the present invention can provide an olefin polymer having an extremely wide molecular weight distribution and high stereoregularity with high activity even if the content of the cyclic ester compound (a) is low. [0131] The propylene-based block copolymer of the present invention is a polymer of a wide molecular weight distribution. The reason is obscure at present, but such a cause as described below can be presumed. [0132] It is known that the cyclic hydrocarbon structure forms various steric structures such as chair form and boat form. If the cyclic structure has a substituent, variations of the steric structures which can be taken are further increased. Moreover, if the bond between a carbon atom to which an ester group (COOR1 group) is bonded and another carbon atom to which an ester group (COOR1 group) is bonded among the carbon atoms to constitute the cyclic skeleton of the cyclic ester compound is a single bond, variations of the steric structures which can be taken are increased. That such various steric structures can be taken as above leads to formation of various active species on the solid titanium catalyst component (I) . As a result, when polymerization of olefins is carried out using the solid titanium catalyst component (I), an olefin polymer having various molecular weights can be preparedat once. That is to say, apropylene-basedblockcopolymer having a wide molecular weight distribution can be prepared. [0133] In the present invention, the cyclic ester compounds (a) and (b) may be formed during the course of preparation of the solid titanium catalyst component (I). For example, in the preparation of the solid titanium catalyst component (I), a step of substantially contacting carboxylic acid anhydrides or carboxylic acid dihalides corresponding to the cyclic ester compounds (a) and (b) with the corresponding alcohol is provided, whereby the cyclic ester compounds (a) and (b) can be incorporated into the solid titanium catalyst component. [0134] In the preparation of the solid titanium catalyst component (I) for use in the present invention, a magnesium compound and a titanium compound are used in addition to the above cyclic ester compounds (a) and (b) . Moreover, the later-descried catalyst component (c) and catalyst component (d) may be used in combination so long as the object of the present invention is not impaired. [0135] Magnesium compound Examples of the magnesium compounds for use in the preparation of the solid titanium catalyst component (I) in the present invention include publicly known magnesium compounds, e.g., magnesium halides, such as magnesium chloride and magnesium bromide; alkoxymagnesium halides, such as methoxymagnesium chloride, ethoxymagnesium chloride and phenoxymagnesium chloride; alkoxymagnesiums, such as ethoxymagnesium, isopropoxymagnesium, butoxymagnesium and 2-ethylhexoxymagnesium; aryloxymagnesiums, such as phenoxymagnesium; and carboxylic acid salts of magnesium, such as magnesium stearate. [0136] These magnesium compounds may be used singly or may be used in combination of two or more kinds . Moreover, these magnesium compounds may be complex compounds or double compounds with other metals, or mixtures with other metal compounds . [0137] Of these, magnesium compounds containing halogen are preferable, and magnesium halide, particularly magnesium chloride, is preferably used. In addition, alkoxymagnesium such as ethoxymagensium is also preferably used. The magnesium compound may be a compound derived from other substances, for example, a compound obtained by contacting an organomagnesium compound with titanium halide, silicon halide, halogenated alcohol or the like, such as Grignard reagent. When alkoxymagnesium is combined with tetraalkoxytitanium or the like, it is preferable to react alkoxymagnesium with silicon tetrachloride or the like as a halogenating agent to convert it into magnesium halide. [0138] Titanium compound The titanium compound is , for example, a tetravalent titanium compound represented by the following formula: wherein R is a hydrocarbon group, X is a halogen atom, and 0≤g≤4. More specifically, there can be mentioned, for example, titanium tetrahalides, such as TiCl4 and TiBr4; alkoxytitaniumtrihalides, suchasTi (OCH3)C13, Ti (OC2H5) Cl3, Ti(O-n-C4H9)Cl3, Ti(OC2H5)Br3 and Ti (O-isoC4H9) Br3; alkoxytitanium dihalides, such as Ti(OCH3)2Cl2 and Ti(OC2H5)2Cl2; alkoxytitanium monohalides, such as Ti(OCH3)3Cl, Ti (O-n-C4H9)3Cl and Ti (OC2H5) 3Br; and tetraalkoxytitaniums, such as Ti(OCH3)4, Ti(OC2H5)4, Ti(OC4H9)4 and Ti(O-2-ethylhexyl)4. [0139] Of these, titanium tetrahalides are preferable, and titanium tetrachloride is particularly preferable. These titanium compounds may be used singly or may be used in combination of two or more kinds. [0140] As such magnesium compounds and titanium compounds, compounds described in detail in, for example, the aforesaid patent literatures 1 and 2 can be also mentioned. [0141] For preparing the solid titanium catalyst component (I) of the present invention, publicly known processes can be used without any restriction, except for using the cyclic ester compounds (a) and (b). Examples of preferred processes include the following processes (P-l) to (P-4). [0142] (P-l) Process comprising contacting a solid adduct composed of a magnesium compound and a catalyst component (c) with the cyclic ester compounds (a) and (b) and a liquid titanium compound in a suspension state in the presence of an inert hydrocarbon solvent. [0143] (P-2) Process comprising contacting a solid adduct composed of a magnesium compound and a catalyst component (c) with the cyclic ester compounds (a) and (b) and a liquid titanium compound plural times. [0144] (P-3) Process comprising contacting a solid adduct composed of a magnesium compound and a catalyst component (c) with the cyclic ester compounds (a) and (b) and a liquid titanium compound plural times in a suspension state in the presence of an inert hydrocarbon solvent. [0145] (P-4) Process comprising contacting a liquid magnesium compound composed of a magnesium compound and a catalyst component (c) with a liquid titanium compound and the cyclic ester compounds (a) and (b). [0146] In the preparation of the solid titanium catalyst component (I), the reaction temperature is preferably in the range of -30°C to 150°C, more preferably -25°C to 140°C, still more preferably -25°C to 130°C. [0147] Preparation of the solid titanium catalyst component (I) may be carried out in the presence of a publicly known medium, when needed. Examples of the media include aromatic hydrocarbons having slight polarity, such as toluene, and publicly known aliphatic hydrocarbons and alicyclic hydrocarbons, such as heptane, hexane, octaner decane and cyclohexane. Of these, aliphatic hydrocarbons are preferred media. [0148] When polymerization reaction of olefins is carried out using the solid titanium catalyst component (I) prepared as above, the effect of obtaining a polymer of a wide molecular weight distribution is compatible with the activity of the catalyst and the high stereoregularity of the resulting polymer at a higher level. [0149] Catalyst component (c) The catalyst component (c) used for forming the solid adduct or the liquid magnesium compound is preferably a publicly known compound capable of solubilizing the aforesaid magnesium compound at a temperature of room temperature to about 300°C, and preferred examples of such compounds include alcohols, aldehydes, amines, carboxylic acids and mixtures thereof. As such compounds, compounds described in detail in, for example, the aforesaid patent literatures 1 and 2 can be mentioned. [0150] Examples of the alcohols having an ability to solubilize the magnesium compound include: aliphatic alcohols, such as methanol, ethanol, propanol, butanol, isobutanol, ethylene glycol, 2-methylpentanol, 2-ethylbutanol, n-heptanol, n-octanol, 2-ethylhexanol, decanol and dodecanol; alicyclic alcohols, such as cyclohexanol and methylcyclohexanol; aromatic alcohols, such as benzyl alcohol and methylbenzyl alcohol; and aliphatic alcohols having alkoxy group, such as n-butyl cellosolve. [0151] Examples of the carboxylic acids include organic carboxylic acids having 7 or more carbon atoms, such as caprylic acid and 2-ethylhexanoic acid. [0152] Examples of the aldehydes include aldehydes having 7 or more carbon atoms, such as capric aldehyde and 2-ethylhexyl aldehyde. [0153] Examples of the amines include amines having 6 or more carbon atoms, such as heptylamine, octylamine, nonylamine, laurylamine and 2-ethylhexylamine. [0154] As the catalyst components (c) , the above alcohols are preferable, and ethanol, propanol, butanol, isobutanol, hexanol, 2-ethylhexanol and decanol are particularly preferable. [0155] The amounts of the magnesium compound and the catalyst component (c) used for preparing the solid adduct or the liquid magnesium compound vary depending upon the types thereof, the contact conditions, etc., but the magnesium compound is used in an amount of 0.1 to 20 mol/liter, preferably 0.5 to 5 mol/liter, based on the unit volume of the catalyst component (c) . Amedium inert to the solid adduct may be used in combination, when needed- Preferred examples of the media include publicly known hydrocarbon compounds, such as heptane, hexane, octane and decane. [0156] The ratio between magnesium in the resulting solid adduct or the liquid magnesium compound and the catalyst component (c) cannot be defined indiscriminately because it varies depending upon the type of the compound used. However, the amount of the catalyst component (c) is preferably not less than 2.0 mol, more preferably not less than 2.2 mol, still more preferably not less than 2 . 3 mol, particularly preferably not less than 2.4 mol but not more than 5 mol, based on 1 mol of magnesium in the magnesium compound. [0157] Aromatic carboxylic acid ester and/or compound having two or more ether linkages through plural carbon atoms The solid titanium catalyst component (I) of the present invention may further contain an aromatic carboxylic acid ester and/or a compound having two or more ether linkages through plural carbon atoms (also referred to as a "catalyst component (d)" hereinafter) . When the solid titanium catalyst component (I) of the present invention contains the catalyst component (d), catalytic activity can be sometimes enhanced, stereoregularity can be sometimes increased, and molecular weight distribution can be sometimes further widened. [0158] As such catalyst components (d) , publicly known aromatic carboxylic acid esters andpolyether compounds which have been preferably used for an olefin polymerization catalyst in the past, such as compounds described in, for example, the aforesaid patent literature 1 and Japanese Patent Laid-Open Publication No. 354714/2001, can be used without any restriction. [0159] Examples of the aromatic carboxylic acid esters include aromatic carboxylic acidmonoesters, such as benzoic acid ester (ethyl benzoate or the like) and toluic acid ester, and aromatic polycarboxylic acid esters, such as phthalic acid esters. Of these, aromatic polycarboxylic acid esters are preferable, and phthalic acid esters are more preferable. As the phthalic acid esters, phthalic acid alkyl esters, such as ethyl phthalate, n-butyl phthalate, isobutyl phthalate, hexyl phthalate and heptyl phthalate, are preferable, and diisobutyl phthalate is particularly preferable. [0160] The polyether compound is more specifically a compound represented by the following formula (3) . [0161] [Chem. 15] (Formula Removed) [0162] In the formula (3) , m is an integer of 1 to l0, morepref erably an integer of 3 to 10, particularlypref erably an integer of 3 to 5. R11, R12 and R31 to R36 are each independently a hydrogen atom or a substituent having at least one element selected from carbon, hydrogen, oxygen, fluorine, chlorine, bromine, iodine, nitrogen, sulfur, phosphorus, boron and silicon. [0163] R11 and R12 are each preferably a hydrocarbon group of 1 to 10 carbon atoms, more preferably a hydrocarbon group of 2 to 6 carbon atoms, and R31 to R36 are each preferably a hydrogen atom or a hydrocarbon group of 1 to 6 carbon atoms. [0164] R11 and R12 are each specifically methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, isopentyl group, neopentyl group, hexyl group, heptyl group, octyl group, 2-ethylhexyl group, decyl group, cyclopentyl group or cyclohexyl group, and they are each preferably ethyl group, n-propyl group, isopropyl group, n-butyl group or isobutyl group. [0165] R31 to R36 are each specifically hydrogen atom, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group or isobutyl group, and they are each preferably hydrogen atom or methyl group. [0166] Arbitrary groups of R11, R12 and R31 to R36, preferably R11 and R12, may form a ring other than a benzene ring in cooperation, and in the main chain, an atom other than carbon may be contained. [0167] Examples of the compounds having two or more ether linkages include: monosubstituted dialkoxypropanes, such as 2-isopropyl-l,3-dimethoxypropane, 2-s-butyl-l,3-dimethoxypropane, and 2-cumyl-l,3-dimethoxypropane; disubstituted dialkoxypropanes, such as 2-isopropyl-2-isobutyl-l,3-dimethoxypropane, 2,2-dicyclohexyl-l,3-dimethoxypropane, 2-methyl-2-isopropyl-l,3-dimethoxypropane, 2-methyl-2-cyclohexyl-l,3-dimethoxypropane, 2-methyl-2-isobutyl-l,3-dimethoxypropane, 2,2-diisobutyl-l,3-dimethoxypropane, 2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane, 2,2-diisobutyl-l,3-diethoxypropane, 2,2-diisobutyl-l,3-dibutoxypropane, 2,2-di-s-butyl-l,3-dimethoxypropane, 2,2-dineopentyl-l,3-dimethoxypropane, 2-isopropyl-2-isopentyl-l, 3-dimethoxypropane, and 2-cyclohexyl-2-cyclohexylmethyl-l,3-dimethoxypropane; dialkoxyalkanes, such as 2,3-dicyclohexyl-l,4-dimethoxybutane, 2,3-dicyclohexyl-l,4-diethoxybutane, 2,3-diisopropyl-l,4-diethoxybutane, 2,4-diphenyl-l,5-dimethoxypentane, 2, 5-diphenyl-l,5-dimethoxyhexane, 2,4-diisopropyl-l,5-dimethoxypentane, 2,4-diisobutyl-l,5-dimethoxypentane, and 2,4-diisoamyl-l,5-dimethoxypentane; trialkoxyalkanes, such as 2-methyl-2-methoxymethyl-l,3-dimethoxypropane, 2-cyclohexyl-2-ethoxymethyl-l,3-diethoxypropane, and 2-cyclohexyl-2-methoxymethyl-l,3-dimethoxypropane; and dialkoxycycloalkanes, such as 2,2-diisobutyl-l,3-dimethoxy-4-cyclohexene, 2~isopropyl-2-isoamyl-l,3-dimethoxy-4-cyclohexene, 2-cyclohexyl-2-methoxymethyl-l,3-dimethoxy-4-cyclohexen e, 2-isopropyl-2-methoxymethyl-l,3-dimethoxy-4-cyclohexene 2-isobutyl-2-methoxymethyl-l,3-dimethoxy-4-cyclohexene, 2-cyclohexyl-2-ethoxymethyl-l,3-dimethoxy-4-cyclohexene 2-isopropyl-2-ethoxymethyl-l,3-dimethoxy-4-cyclohexene, and 2-isobutyl-2-ethoxymethyl-l,3-dimethoxy-4-cyclohexene. [0168] Of these, preferable are 1,3-diethers, and particularly preferable are 2-isopropyl-2-isobutyl-l, 3-dimethoxypropane, 2, 2-diisobutyl-l,3-dimethoxypropane, 2-isopropyl-2-isopentyl-l/3-dimethoxypropane, 2,2-dicyclohexyl-l,3-dimethoxypropane and 2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane. [0169] These compounds may be used singly or may be used in combination of two or more kinds. [0170] The cyclic ester compounds (a) and (b) , the catalyst component (c) and the catalyst component (d) may be considered to be long to components called electron donors by persons skilled in the art. It is known that the electron donor components exhibit an effect of enhancing stereoregularity of the resulting polymer, an effect of controlling composition distribution of the resultingpolymer, a coagulant effect of controllingparticle shape or particle diameter of catalyst particles, etc., with maintaining high activity of the catalyst. [0171] It is thought that the cyclic ester compounds (a) and (b) further exhibit an effect of controlling a molecular weight distribution because they themselves are electron donors. [0172] In the solid titanium catalyst component (I) of the present invention, the halogen/titanium ratio by atom (i.e., number of moles of halogen atom/number of moles of titanium atom) is desired to be in the range of 2 to 100, preferably 4 to 90, the cyclic ester compound (a)/titanium ratio by mol (i.e., number of moles of cyclic ester compound (a)/number of moles of titanium atom) and the cyclic ester compound (b)/titanium ratio by mol (i.e., number of moles of cyclic ester compound (b)/number of moles of titanium atom) are desired to be each in the range of 0.01 to 100, preferably 0.2 to 10, and the catalyst component (c)/titanium atom ratio by mol is desired to be in the range of 0 to 100, preferably 0 to 10. [0173] Preferred ratios between the cyclic ester compound (a) and the cyclic ester compound (b) are as follows. The lower limit of the value (% bymol) of 100 x cyclic ester compound (a)/(cyclic ester compound (a) + cyclic ester compound (b)) is 5% by mol, preferably 25% by mol, more preferably 40% by mol, particularly preferably 50% by mol. The upper limit thereof is 99% by mol, preferably 90% by mol, more preferably 85% by mol, particularly preferably 80% by mol. [0174] The magnesium/titanium ratio by atom (i.e., number of moles of magnesium atom/number of moles of titanium atom) is desired to be in the range of 2 to 100, preferably 4 to 50. [0175] The content of the components which may be contained in addition to the aforesaid cyclic ester compounds (a) and (b) , such as the catalyst component (c) and the catalyst component (d), is preferably not more than 20% by weight, more preferably not more than 10% by weight, based on 100% by weight of the cyclic ester compounds (a) and (b). [0176] As the more detailed conditions for preparing the solid titanium catalyst component (I), the same conditions as described in, for example, EP585869A1 (European Patent Laid-Open Application No. 0585869) and the aforesaid patent literature 2 can be preferably used, except for using the cyclic ester compounds (a) and (b). [0177] Organometallic compound catalyst component (II) The organometallic compound catalyst component (II) is an organometallic compound containing a metal atom selected from Group 1, Group 2 and Group 13 of the periodic table. Specifically, a compound containing a Group 13 metal, such as an organoaluminum compound, an alkylate of a complex of a Group 1 metal and aluminum, an organometallic compound of a Group 2 metal, etc. can be used. Of these, an organoluminum compound is preferable. [0178] Preferred examples of the organometallic compound catalyst components (II) include organometallic compound catalyst components described in publicly known literatures such as the aforesaid EP585869A1. [0179] Electron donor (III) The olefin polymerization catalyst of the present invention may further contain an electron donor (III) whenneeded, inaddition to the above organometallic compound catalyst component (II) . The electron donor (III) is preferably an organosilicon compound. The organosilicon compound is, for example, a compound represented by the following formula (4): [0180] wherein R and R' are each a hydrocarbon group, and n is an integer of 0