Technical Field The present invention relates to a method for m a n u f a c ~ ga shaped product constituted by a fiber-reinforced composite material formed from a random mat inciuding reinforcing fibers and a thermoplastic resin, the random mat is a starting material. More specifically, the present invention relates to a method for manufacturing a shaped product, the method capable of obtaining a shaped product with maintained isotropy of the reinforcing fibers to the end thereof even in a case of being press-molded by closing a mold under a condition in which the charge ratio of a prepreg to the mold is 100% or less. [Background Art] A fiber-reinforced composite material in which carbon fibers, aramid fibers, glass fibers or the like are used as reinforcing fibers has been widely utilized for structural materials of aircrafts, vehicles or the like, or in generd industries and sports such as a tennis racket, a golf club shaft and a fishing rod by utilizing high specific strength and high specific elasticity thereof. In molding a shaped product constituted by the fiber-reinforced composite material, it has been proposed that base materids including discontinuous reinforcing fibers and a resin are layered to prepare a prefom, the preform is arranged in a wider range than a total mold cavity area, and the perform is press-molded (See Patent Document 1). However, in this moIdig method, the outer periphery portion of the shaped product is required to be trimmed. For this reason, a large amount of offcuts are produced, and the disposal thereof incurs costs. In order to obtain an integrated shaped product that substantially exhibits isotropy, it must be careful to ensure that symmetrically layering is always made, and thus the discretion degree of the time for preparing perform and the arrangement method in moIding is low. Also, a method of obtaining a shaped product constituted by a fiber-reinforced composite by molding a composition including reinforcing fibers and a resin through injection molding is performed (See, Patent Document 2). However, this method employs so-called long fiber composite peIlets, in which an average length of the reinforcing fibers ranges fkom about 5 mm to 15 mm, and the length of the reinforcing fibers is largely reduced in the shaped product after the injection molding. [Citation List] [Patent Document] [Patent Docummt 11 Japanese Patent Laid-Open Publication No. 20 10-25393 8 [Patent Document 21 Japanese Patent Laid-Open Publication H04-193 504 [Summary of Invention] [Problems to be Solved] An object of the present invention is to provide a method for manufacturing a shaped product from a random mat including re~orcingfi bers and a thermoplastic resin, the method which may obtain a shaped product in which isotropy of the reinforcing fibers is maintained to the end thereof even in a case of being press-molded under a condition in which the charge ratio of a prepreg to a mold is low. [Means for Solving the Problems] The inventors of the present invention found that the above-described problem may be solved when a prepreg obtained by impregnating a specific random mat type of reinforcing fibers with a thermoplastic resin is molded under a specific condition, and then completed the present invention. That is, the present invention provides a method for manufacturing a shaped product constituted by a fiber-reinforced composite material, the method including: 1) a prepreg preparation step of obtaining a prepreg in which a random mat including reinforcing fibers with an average fiber length of 5 mm to 100 mm and a thermoplastic resin is heated up to a temperature of a melting point or more and Iess than a thermal decomposition temperature in a case where the thennoplastic resin is crystalline, or up to a temperature of a glass transition temperature or more and less than a thermal decomposition temperature in a case where the thermoplastic resin is amorphous such that the random mat is impregnated with the thermoplastic resin; 2) a prepreg arranging step in which the prepreg that is set at the temperature of the melting point or more and less than the thermal decomposition temperature in the case where the thermoplastic resin is crystalline, or at the temperature of the glass transition temperature or more and less than the thermal decomposition temperature in the case where the thennopiastic resin is amorphous is arranged in a mold which is controlled to a temperature Iess than the melting paint temperature in the case where the thermoplastic resin is crystalline or a temperature less than the glass transition temperature in the case where the thermoplastic resin is amorphous such that a charge ratio represented by equation (3) is 50% or more and 100% ox less; and 3) a molding step in which the prepreg is pressurized within the mold and at the same time, the molding is completed at a temperature less than the melting point in the case where the thermoplastic resin is crystalline, or at a temperature Iess than the glass transition temperature in the case where the thermoplastic resin is amorphous, to obtain the shaped product, in which the random mat includes the reinforcing fibers which are substantially twodimensionally randomly oriented at a fiber anal weight of 25 g/m2 to 10000 dm2, reinforcing fiber bundles (A) constituted by the reinforcing frbers of a critical single fiber number or more, the critical single fiber number defined by equation (I), ate included in an amount of 20 Vol% or more and less than 99 Vol% with respect to the total amount of the reinforcing fibers in the random mat, and an average number of the reinforcing fibers 0 in the reinforcing fiber bundles (A) satisfies equation (2). critical single fiber numbe1=600/D (1) 0.7~140 2 [Manufacturing of Random Mat] As reinforcing fibers, carbon fibers "Tenax" (registered trademark) STS40-24KS (average fiber diameter 7 pm, fiber width 10 mm, tensile strength 4,000 MPa) manufactured by TOHO TENAX Co., Ltd were used. The carbon fibers were cut into a length of 20 rnm while being extending, and then introduced into a tapered tube at the carbon fiber supply amount of 300 g/min. Within the tapered tube, air was sprayed to the carbon fibers at a wind velocity of 450 m/sec such that the fiber bundles were partially fiber-opened and the partially fiber-opened fiber bundles were sprayed on a table capable of moving in XY directions, the table provided below the outlet of the tapered tube while being suction4 by a blower from the bottom of the table. A poIyamide 6 resin (A1030, manufactured by Unitika Limited) as a matrix resin was supplied into the tapered tube at 360 ah, and was sprayed simultaneously with the carbon fibers to obtain a random mat with a thickness of 7.5 mm in which the carbon fibers with the average fiber length of 20 mm were mixed with PA6. The fiber areal weight of the reinforcing fibers in the obtained random mat was 370 dm2. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of fibers (N) were investigated, the critical single fiber number defined by equation (1) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 35 Vol%, and the average number of the fibers (N) in the reinforcing fiber bundles (A) was 240. The manufacturing conditions and measurement/evaluation results of the random mat are represented in Table 1. Table 1 [Prepreg Preparation Step] The obtained random mat was heated up to 2S0°C, and pressurized at a pressure of 3 MPa for 7 minutes, and cooled to 80°C to obtain a plate-shaped prepreg, with a thickness of 1.5 mm. The void &tion of the prepreg was 0.09%. The manufactwing conditions and rneasurement/evaluation results of the prepreg are repmented in Table 2. Table 2 [Prepreg hanging Step] Two prepregs that were cut out to be 80% with respect to the mold cavity projection area were placed into an hfkred oven and heated at 25S°C, and then layered, and arranged within a flat plate mold of which temperature was controlled to 130°C and a clearance of ends was 0.02 mrn (FIG. 1). [Molding Step] Press-molding was performed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 2.4 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were detemined to be filled up to ends of the mold. The schematic view of the obtained shaped product is illustrated in FIG. 3. The portion indicated by 5 is a charged portion of the base material (prepreg) within the mold, and the outer portion thereof indicated by 6 is a portion where the base material (prepreg) flowed to edges of the mold cavity. In tJ~ep ortions indicated by 7 in the drawing, when volume fractions (Vf) of the reinforcing fibers were investigated, respectively, the average of the flow portion was 35.2%, and the charged potion of the base materid (prepreg) was 35.0%, that is, the flow portion and the base material (prepreg) charged potion had almost the same values. In. the flow portion indicated by 8 in the drawing, when the tensile modulus was measured, the ratio (E6) obtained by dividing a larger one by a smaller one among the tensile modulus in two directions perpendicular to each other was 1.03, and isotropy was determined to be maintained. When the thickness variation of the obtained shaped product was evaluated, the thickness was codltrned to be almost uniform. The evaluation result of the thickness variation is represented in Table 3. The manufacturing conditions and measurernentlevaluation results of the shaped product are shown in Table 2. Table 3 Thickness (Measurement value) Variation of thickness [Manufacturing of Random Mat] A random mat with a thickness of 4.0 mm was obtained under the same conditions as in ExarnpIe 1 except that the supply amount of carbon fibers was 150 g/min, the supply amount of polyamide 6 resin was 180 ghin, and the wind velocity within the tapered tube was 200 dsec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 185 1Jrn2. in the obtained nmdom mat, when the ratio of the reinforcing fiber b d e s (A), and the average number of the fibers (N) were investigated, the critical single fiber number defined by equation (1) was 86, the ratio of the reidorcing fiber bundles (A) with respect to the totd amount of the fibers in the random mat was 35 Vol%, and the average number of the fibers (N) in the reinforcing fiber bundles (A) was 240. The manufacturing conditions and measurement~evaluatiorne sults of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 0.8 mm in the same rnanner as in Example 1. The void fraction of the prepreg was 0.3%. The manufacturing conditions and measurement~evaluation results of the prepreg are represented in Table 2. [P*P~% -gkg Step1 Four prepregs that were cut out to be 80% with respect to the mold cavity projection area were layered, placed into an infrared oven and heated at 255"C, and then arranged within a three-dimensional shaped mold (as illustrated in FIG. 2) of which a temperature was controlled to 130°C and a clearance of ends was 0.05 mm (FIG. 4). [Molding Step] Press-molding was paformed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 2.4 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a h c e appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. The schematic view of the obtained shaped product is illustrated in FIG. 5. The portion indicated by 5 is a charged portion of the base material (prepreg) within the mold, and the outer portion thereof indicated by 6 is a portion where the base material (prepreg) flowed to edges of the mold cavity. In the portions indicated by 7 in the drawing, when volume fractions (Vf) of the reinforcing fibers were investigated, respectively, the average of the flow portion was 35.3%, and the charged potion of the base material (prepreg) was 35.0%, that is, the flow portion and the base material (prepreg) charged potion bad almost the same values. In the flow portion indicated by 8 in the drawing, when the tensile modulus was measured, the ratio (a)ob tained by dividing a larger one by a smaller one among the tensile modulus in two directions perpendicdar to each other was 1.08, and isotropy was determined to be maintained. The manufacturing conditions and measurement/evaluation results of the shaped product are represented in Table 2. [Manufacturing of Random Mat] As reinforcing fibers, carbon fibers (manufactured by TOHO TENAX Co., Ltd.: TENAX IMS60-12K (avmge fiber diameter 5 pm, fiber width 6 mm)) were used. The carbon fibers were cut into a length of 20 mm while h g extended, and then introduced inta a tapered tube at the carbon fiber supply amount of 100 g/min.. Within the tapered hrbe, air is sprayed to the carbon fibers at a wind velocity of 250 m/sec such that the fiber bundles were partially fiber-opened and the partially fiber-opened fiber bundles were sprayed on a table capable of moving in XY directions provided below the outlet of the tapered tube while being suctioned by a blower fiom the bottom of the table. A polycarbonate resin (mufactwed by Teijin Chemicals Ltd., Paalite (registered trademark) L-1225L) as a matrix resin was supplied into the tapered tube at 300 g/mind and was sprayed simultaneously with the carbon fibers to obtain a mdom mat with a thickness of about 5.0 mm in which the carbon fibers with the average fiber length of 20 mm were mixed with pol ycarbonate. The fiber areal weight of the reinforcing fibers in the obtained random mat was 125 g/m2. In the obtained mdom mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers (N) were investigated, the critical single fiber number defined by equation (1) was 120, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 80%, and the average number of the fibers (N) in the reinforcing fiber bundles (A) was 1000. The manufacturing conditions and rneasurement/evaluation results of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was heated up to 260°C, and pressurized at a pressure of 5 MPa for 7 minutes, and cooled to 50°C to obtain a prepreg with a thickness of 1.0 mm. The void fraction of the prepreg was 0.2%. The manufacturing conditions and measurementlevaluation results of the prepreg are represented in Table 2. [Prepreg Arranging Step] Two base material sheets (prepregs) that were cut out to be 50% with respect to the mold cavity projection area were placed into an i n h e d oven and heated at 260°C, and then layered, and arranged within a flat plate mold of which a temperature was controlled to 60°C, and a clearance of ends was 0.02 mrn (FIG. 1). [Molding Step] Press-molding was performed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 1.0 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. The schematic view of the obtained shaped product is illustrated in FIG. 3. The portion indicated by 5 is a charged portion of the base materia1 (prepreg) within the mold, and the outer portion thereof indicated by 6 is a portion where the base material (prepreg) flowed to edges of the mold cavity. In the portions indicated by 7 in the drawing, when volume firactions (Vf) of the reinforcing fibers were investigated, respectively, the average of the flow portion was 19.9%, and the charged potion of the base material (prepreg) was 20.1%, that is, both had almost the same values. When the tensile modulus was measured, the ratio (Elt) obtained by dividing a larger one by a smaller one among the tensile modulus in two directions perpendicular to each other was 1.2 1, and isotropy was determined to be maintained. The manufacturing conditions and measurementlevaluation results of the shaped product are represented b Table 2. [Manufacturing of Random Mat] A random mat with a thickness of 15.0 mm was obtained under the same conditions as in Example 1 except that the supply amount of carbon fibers was 600 g/min, the supply amount of polyamide 6 resin was 720 g/min, and the wind velocity within the tapered tube was 1000 dsec. The fiber areal weight af the reinforcing fibers in the obtained random mat was 740 g/m2. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers (N) were investigated, the critical single fiber number defined by equation (1) was 86, the ratio of the reinforcing fiber bundIes (A) with respect to the total amount of the fibers in the random mat was 35 VoI%, and the average number of the fibers (N) in the reiinforcing fiber bundles (A) was 240. The manufacturing conditions and rneasurernent/evaluation d t s of the randorn mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was us& to obtain a plate-shaped prepreg with a thickness of 3.0 mm in the same manner as in Example 1. The void &action of the prepreg was 0.5%. The manufacturing conditions and rnaamement/evaIuation results of the prepreg are represented in Table 2. [Prepreg Arranging Step] Two prepregs that were cut out to be 80% with respect to the mold cavity projection area were placed into an inbred oven and heated at 25S°C, and then layered, and m g e d with a ribboss shaped mold of which a temperature was controlled to 1 30°C and a clearance of ends was 0.08 mm (FIG. 6). [MoIding Step] Press-molding was performed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 4.8 mm. In the obtained shaped product, no material cracks or wrinkles occmed, a surface appearance was good, no product waqage was found, and the resin and the fibers were determined to be filled up to ends of the mold. The schematic view of the obtained shaped product is illustrated in FIG. 7. The portion indicated by 5 is a charged portion of the base materia1 (prepreg) within the mold, and the outer portion thereof indicated by 6 is a portion where the base material (prepreg) flowed to edges of the mold cavity. In the portions indicated by 7 in the drawing, when volume fractions (Vf) of the reinforcing fibers were investigated, respectively, the average of the flow portion was 34.6% and the charged potion of the base material (prepreg) was 34.8%, that is, both had almost the same values. When the tensile modulus of the flow portion was measured, the ratio (E6) obtained by dividing a larger one by a smaller one among tensile modulus in two directions perpendicular to each other was 1.09, and isotropy was determined to be maintained. The manufacturing conditions and measurement/evaluation resuits of the shaped product are represented in Table 2. [Manufacturing of Random Mat] A random mat with a thickness of 7.0 mm was obtained under the same conditions as in Example I except that the supply amount of carbon fibers was 300 g/min, the supply amount of poIyamide 6 resin was 360 g/min, and the wind velocity w i t h the tapered tube was 400 dsec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 370 dm'. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers (N) were investigated, the Mitical single fiber number defined by equation (I) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 50 V01%, and the average number of the fibers (N) in the .reidorcing fiber bundles (A) was 500. The manufacturing conditions and measurementlevaluation results of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 1.5 mm in the same manner as in Example 1. The void fraction of the prepreg was 0.3%. The manufacturing conditions and measurementlevaluation results of the prepreg are represented in Table 2. [Prepreg furaging Step and Molding Step] Arrangement of the prepreg and molding of a shaped product were performed in the same manner as in Example 1 ta obtain the shaped product wit& a thickness of 2.4 mm. In the obtained shaped product, no materia1 cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. When the volume firaction (Vf) of the reinforcing fibers was investigated, the average of the flow portion was 34.9%, and the charged potion of the base material (prepreg) was 35.2%, that is, both had almost the same values, When the tensile modulus of the flow portion was measured, the ratio (E6) obtained by dividing a larger one by a smaller ane among the tensile modulus in two directions perpendicular to each other was 1.02, and isotropy was determined to be mainbind. The manufacturing conditions and measuxement~evaluation results of the shaped product are ;represented in Table 2. [Manufacturing of Random Mat] A random mat with a tbiclcness of 4.0 mm was obtained under the same conditions as in Example 1 except that the supply amount of carbon fibers was 100 g/min, the supply amount of polyamide 6 resin was 300 g/min, and the wind velocity within the tapered tube was 250 rn/sec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 125 dm2. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fi'bers (N) were investigated, the critical single fiber number deflned by equation (1) was 86, ihe ratio of the reinforcing fiber bundles (A) with respect to the total maunt of the fibers in the random mat was 80 Vol%, and the average number of the fibers (N) in the reinforcing fiber bundles (A) was 1000. The manufacturing conditions and measurernent/evduation results of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 1.0 rnm in the same manner as in ExampIe I. The void hction of the prepreg was 0.3%. The rnanufachuing conditions and measurement/evaluation results of ihe prepreg are represented in Table 2. [Prepreg Arranging Step] Two prepregs that were cut out to be 50% with respect to the mold cavity projection area were placed into an infiard oven and heated at 255"C, and then layered, and arranged within a flat plate mold of which a temperature was controlled to 130°C and a clearance of ends was 0.02 mm (FIG. 1). [Molding Step] Press-molding was performed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 1.0 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. When volume hetion (Vf) of the re~orcingfi bers was investigated, the average of the flow portion was 18.0%, and the charged potion of the base material (prepreg) was 18,2%, that is, both had almost the same values. When the tensile modulus of the flow portion was measured, the ratio (E8) obtained by dividing a larger one by a smaller one among the, tensile modulus in two directions perpendicular to each other was 1.10, and isotropy was determined to be maintained. The rnanufsturing conditions and measurementlevaluation results of the shaped product are represented in Table 2. [Manufacturing of Random Mat] As reinforcing fibers, carbon fibers 'Tenax" (registered trademark) STS40-24KS (average fiber diameter 7 p, fiber width 10 mm) manufactured by TOHO TENAX Co., Ltd were used. The fibers were slit into a width of 2 mm or less by using a vertical sIitter, and cut into a fiber length of 20 mm. As a cutter, a rotary cutter that is capable of continuously cutting the reinforcing fiber bundles was used. The strand that had passed though the rotary cutter was introduced a tapered tube, and processed at a wind velocity of 250 dsec to partially fiber-open the fiber bundles. Then, they were sprayed on a table capable of moving in XY directions provided below the outlet of the tapered tube while being suctioned by a blower from the bottom of the table, and thus a mat with a thickness of about 4 mm was formed. Then, a molten matrix resin was supplied to the obtained mat. As the matrix resin, a polyamide 6 resin (A1030) manufactured by Unitika Limited was used. This was molten by an extruder and the molten resin was supplied to the entire d a c e of the mat from a T-die. Here, the portion on the mat surface to which the resin is supplied was heated by an infrared heater so as to suppress the resin from being cooled and solidified. The device was driven at the polyamide 6 resin supply amount of 300 &in with respect to the reinforcing fiber supply amount of 100 @in, to form a random mat constituted by the reinforcing fibers and the thermoplastic resin. The fiber areal weight of the reinforcing fibers in the obtained random mat was 125 dm2. In the obtained random mat, when the ratio of the reinforcing fiba bundles (A), and the average number of the fibers (N) were investigated, the criticaI single fiber number defined by equation (1) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 80%, and the average number of the fibers 0 in the reinforcing fiber bundles (A) was 1000. The manufacturing conditions and measurement/evaluation results af the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was heated and pressurized by a couple of heating rollers set to 280°C to prepare a prepreg impregnated with the resin. The cooled prepreg had a thickness of 1.0 mm, and a void hction of 0.6%. The manufacturing conditions and measurernant/evaluation results of the prepreg are represented in Table 2. [Prepreg Arranging Step] Two base material sheets that were cut out to be 50% with respect to the mold cavity projection area were placed into an i&md oven and heated at 255*C, and then layered, and arranged within a flat plate mold of which a temperature was controlled to 130°C and a clearance of ends was 0.02 mm (FIG. 1). [Molding Step] Press-molding was performed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 1.0 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. When volume fiaction (Vf) of the reinforcing fibers was investigated, the average of the flow portion was 18.0%, and the charged potion of the base mated (prepreg) was 18. I%, that is, both had almost tbe same values. When the tensile modulus was measured, the ratio (E6) obtained by dividing a larger one by a smaller one among fhe tensile modulus in two directions perpendicular to each other was 1.13 and isotropy was determined to be maintained. The manufacturing conditions and measurementlevaluation resubs of the shaped product are represented in Table 2. [Manufactwring of Random Mat] A random mat with a thickness of 7.0 mm was obtained under the same conditions as in Example 1 except that the average fiber length of the reinforcing fibers was 10 mm, and the wind velocity within the tapered tube was 50 mlsec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 370 g/m2. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers 0 were investigated, the critical single fiber number defined by equation (I) was 86, the ratio of the resorting fiber bundles (A) with respect to the total amount of the fibers in the random mat was 95 Val%, and the average number of the fibers (N) in the reinforcing fiber bundles (A) was 1200. The manufacturing conditions and measurementlevaluation results of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 1.5 mm in the same mmer as in Example 1. The void fraction of the prepreg was 0.2%. The manufacturing conditions and measurernent/evaluation results of the prepreg are represented in Table 2. [Prepreg Arranging Step and Molding Step] Anangment of the prepreg and molding a shaped product were performed in the same manner ts in Example I to obtain the shaped product with a thickness of 2.4 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. When volume fraction (Vf) of the reinforcing fibers was investigated, the average of the flow portion was 35.0%, and the charged potion of the base material (prepreg) was 35.3%, that is, both had almost the same values. When the tmile modulus of the flow portion was measured, he ratio (E6) obtained by dividing a larger one by a smaller one among the tensile modulus in two directions perpendicular to each other was 1. If, and isotropy was determined to be maintained. The manufacturing canditions and measurement/evaluation results of the shaped product are represented in Table 2. [Manufacturing of Random Mat] A random mat with a thickness of 7.0 mm was obtained under the same conditions as in Example I except that the average fiber length of the reinforcing fibers was 40 mm, and the wind velocity within the tapered tube was 250 dsec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 370 dm2. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers (N) were investigated, the critical single fiber number defined by equation (I) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 80 Val%, and the average number of the fibers (N) in the reinforcing fiber bundIes (A) was 1000. The manufacturing conditions and rneasurernent/evaluation results of the random mat are represented in Table I. prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 1.5 rnm in the same manner as in Example 1. The void hction of the prepreg was 0.4%. The manufacturing conditions and meamement(evaluation results of the prepreg are represented in Table 2. [Prepreg Arranging Step and Molding Step] h g e m e n t of the prepreg and molding a shaped product were performed in the same manner as in Example 1 to obtain the shaped product with a thickness of 2.4 mm. In the obtained shaped product, no material cracks or wrinkles occmed, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. When volume fraction of the reinforcing fibers was investigated, the average of the flow portion was 34.8%, and the charged potion of the base material (prepreg) was 35.1%, that is, both had almost the same values. When the tensile modulus of the flow portion was measured, the ratio (E6) obtained by dividing a larger one by a srndler one among the tensile moduius in two directions perpendicular to each other was 1.05, and isotropy was determined to be maintained. The manufacturing conditions and measurement/evaluation results of the shaped product are represented in Table 2. [Manufacturing of Random Mat] As reinforcing fibers, glass fibers manufactured by Nippon Electric Glass Co., Ltd., EX-2500 (average fiber diameter 15 p, fiber width 9 mm), were used. The glass fibers were cut into a length of 50 mrn while extended, and then introduced into a tapered tube at the glass fiber supply amount of 300 g/min. Within the tapered tube, air is sprayed to the glass fibers at a wind velocity of 300 dsec such that the fiber bundles were partially fiber-opened and the partially fiber-opened fiber bundles were sprayed on a table capable of moving in XY directions provided below the outlet of the tapered tube while being suctioned by a btawer from the bottom of the table. Then, a polyamide 6 resin (A1030, manufactured by Unitika Limited) as a matrix resin was supplied into the tapered tube at 360 glmin, and was sprayed simultaneously with the glass fibers to obtain a mdom mat with a thickness of about 6.5 mm in which the glass iibers with the average fiber length of SO mm was mixed with PAS. The fiber area1 weight of the reinforcing fibers in the obtained random mat was 370 dmZ. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers (N) were investigated, the critical single fiber number defined by equation (1) was 40, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 80%, and the average number of the fibers in the reinforcing fiber bundles (A) was 150. The manufacturing conditions and measurement/evaluation results of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was heated up to 250°C, and pressurized at a pressure of 3 MPa for 5 minutes, and cooled to 80°C to obtain a plate-shaped prepreg with a thickness of 1.5 mm. The void fkaction of the prepreg was 0.1%. The manufacturing conditions and measurementlevaluation results of the prepreg are represented in Table 2. [Prepreg Arranging Step and Molding Step] Arrangement of the prepreg and molding a shaped product were performed in the same manner as in Example 1 to obtain the shaped product with a thickness of 2.4 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filled up to ends of the mold. When volume fraction (Vf) of the reinforcing fibers was investigated, the average of the flow portion was 27.0%, and the charged potion of the base material @repreg) was 27.3%, that is, both had almost the same values. When the tensile modulus of the flow portion was measured, the ratio (E6) obtained by dividing a larger one by a smaller one among the tensile modulus in two directions perpendicular to each other was 1.25, and isotropy was determined to be maintained. The manufacturing conditions and rneasurement/evaluation results of the shaped product are represented in Table 2. [Prepreg Arranging Step] Two prepregs obtained fkom Example 1 which were cut out to be 50% with respect to the mold cavity projection area were placed into an infrared oven and heated at 255OC, and manged witbin a flat plate mold of which a temperature was controlled to 13QQC, and a clearance of ends was 0.02 mm such that one side of each end portion was overlapped by about 30 mrn as iIlustrated in FIG. 9. The charge ratio of the base materials (prepregs) after the overlapping arrangement was 95% with respect to the mold cavity projection area. [Moiding Step] Press-molding was performed at a pressure of 10 MPa for 30 sec to obtain a shaped product with a thickness of 1.5 mm. In the obtained shaped product, no material cracks or wrinkles occurred, a surface appearance was good, no product warpage was found, and the resin and the fibers were determined to be filIed up to ends of the mold. For volume hction (Vf) of the reinforcing fibers, the average of the flow portion was 34.594, and the charged potion of the base material (prepreg) was 35.1%, that is, both had almost the same values. When the tensile modulus of the flow portion was memd, the ratio (E6) of the tensile modulus in two directions perpendicular to each other was 1.10, and isotropy was determined to be maintained. When the tensile test was performed on the base material overlapping portion, the tensile strength of the overlapping portion was not significantly different from other portions. The manufacturing conditions and measurementievaluation results of the shaped product are represented in Table 2. [Manufacturing of Random Mat] A random mat with a thickness of 8.0 mm was obtained under the same conditions as in Example 1 except that the wind velocity within the tapered tube was 700 m/sec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 370 g/m2. in the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers (N) were investigated, the critical single fiber number defined by equation ( 2 ) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 10 Vol%, and the average number of the fibers (N) in the reinforcing fiber bundles (A) was 100. The manufacturing conditions and measurement/evaluation results of the random mat are represented in Table 1. [Prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 1.7 rnm in the sme manner as in Example 1. The void fraction of the prepreg was 10.5%. The manufacturing conditions and measuremmt/evaIuation results of the prepreg are represented in Table 2. [Prepreg Arranging Step aud Molding Step] Arrangement of the prepreg and molding a shaped product were performed in the same manner as in Example 1 to obtain the shaped product with a thickness of 3.0 mm. In the obtained shaped product, materials were not spread up to the end thereof, and thus defect portions were observed. The manufacturing conditions and measurement/evaluation results of the shaped product are represented in Table 2. A random mat with a thickness of 6.5 mm was obtained under the same conditions as in Example 1 except that the wind velocity within the tapered tube was 10 m/sec. The fiber areal weight of the reinforcing fibers in the obtained random mat was 370 g/m2. In the obtained random mat, when the ratio of the reinforcing fiber bundles (A), and the average number of the fibers IN) were investigated, the critical single fiber number defixxed by equation (I) was 86, the ratio of the reinforcing fiber bundles (A) with respect to the total amount of the fibers in the random mat was 100 Vol%, md the average number of the fibers (N) in the reinforcing fiber bundles (A) was 3000. The manufacturing conditions a d measurementlevaluation results of the random mat are represented' in Table 1. [Prepreg Preparation Step] The obtained random mat was used to obtain a plate-shaped prepreg with a thickness of 1.5 mm in the same manner as in Example 1. The void fraction of the prepreg was 3.8%. The manufacturing conditions and measumnent,evaluation results of the prepreg we represented in Table 2. [Prepreg Arranging Step and Molding Step] Arrangement of the prepreg and molding a shaped product were performed in the same manner as in Example 1 to obtain the shaped product with a thickness of 2.4 mm. The maldability, and the surface appearance af the obtained shaped product were good, and no product warpage was found. However, for volume fraction (Vf) of the reinforcing fibers, the average of the flow portion was 33.7%, and the charged potion of the base materid (prepreg) was 35.5%. When the tensile modulus of the flow portion was rnertsured, the ratio (E6) of the tensile modulus in two directions perpendicular to each other was 1.38 and anisotropy was observed. The manufacturing conditions and measurement/evaluation results of the shaped product are represented in Table 2. Industrial Applicability The shaped product including reinforcing fibers and a thermoplastic resin, the shaped product obtained by the manufhctwing method of the present invention, is lightweight and has a shape flexibility, and thus may be a shaped product with maintained isotropy of .the fibers to the end thereof even if press-molded under conditions in which the charge ratio of a prepreg to a mold is low. Further, it is excellent in moldability, thinness, specific rigidity, productivity, and economy, and thus may be effectivdy used in electsicd/electronic components or housings such as electricaVelectronic device parts, automotive parts, personal computers, OA devices, AV devices, mobile phones, phones, facsimiles, household appliances, toy products. Especially, it may be preferabIy used in autamotive parts to be mounted in environmentally friendly automobiles. 1: prepreg, 2: mold cavity, 3: mold cavity edge, 4: total mold cavity area, 5: base materia1 (prepreg) charged potion, 6: flow portion, 7: meammt point of Vf, 8: measurement point of tensile moduius, 9: boss-shaped portion, 10: rib-shaped portion, 11: draft angle of mold ends, 12: clearance of mold, 13: overlapping portions of prepregs We Claim: I. A method for manufacturing a shaped product constituted by a fiberreinforced composite material, the method comprising: 1) a prepreg preparation step of obtaining a prepreg, the prepreg preparation step in which a random mat including reidorcing fibers with an average fiber length of 5 mm to 100 mm and a thermophstic resin is heated up to a temperature of a melting point or more and less than a thermal decomposition temperature in a case where the thermoplastic resin is crystalline, or up to a temperature of a glass transition temperature or more and less than a thermal decomposition temperature in a case where the thermoplastic resin is amorphous such that the random mat is impregnated with the thermoplastic resin, 2) a prepreg arranging step in which the prepreg that is set at the temperature of the melting point or more and less than the thermal decomposition temperature in the case where the thermoplastic resin is crystalline, or at the temperature of the glass transition temperature or more and less than the thema1 decomposition temperature in the case where the thermoplastic resin is amorphous is arranged in a mold to be a charge ratio represented by equation (3) is 50% or more and 100% or less, the mold which is controlled to a temperature less than the melting point temperature in the case where the thermoplastic resin is crystalline or a temperature less than the glass transition temperature in the case where the thermoplastic resin is amorphous; and 3) a molding step in wbich the prepreg is pressurized within the mold and at the same time, the motding is completed at a temperature less than the melting point in the case where the thermoplastic resin is crystalline, or at a temperature less than the. glass transition temperature in the case where the thermoplastic resin is amorphous, to obtain the shaped product, wherein the random mat includes the reinforcing fibers which are substantially twodimensionally randomly oriented at a ftbg areal weight of 25 g/m2 to 1 WOO gh2, reinforcing fiber bundles (A) constituted by the reSorcing fibers of a critical single fiber number or more, the critical single iiber number defined by equation (I), are included in an amount of 20 Vol% or more and less than 99 Vol% with respect to a total mount of the reinforcing fibers in the random mat, and an average number of the reinforcing fibers (N) in the reinforcing fiber bundles (A) satisfies equation (2): critical single fiber numbe1=600/D (1) 0.7~140/ D 2 < ~ < 1 ~ 1 0 ~ 4 3 ~ (2) wherein, in equation (1) and equation (21, D represents an average fiber diameter (p.m) of single reinforcing fibers: charge ratio (%) = 100 x [base material area (mm2)/mold cavity projection area (m211 (3) wherein, in equation (3), a base material area represents a projection area of all the arranged prepreg in a drat3 direction, and a mold cavity projection area represents a projection area in the drafi direction. 2. The method according to claim 1, wherein a content of the thermoplastic resin in the random mat is 50 parts to 1,000 parts by mass with respect to 100 parts by mass of the reinforcing fibers. 3. The method according to claim Z or 2, wherein in the prepreg ammging step, a temperature of the mold is controlled to a temperature of the melting point-200°C or more and the melting point-I O°C or less in the case where the thermoplastic resin is crystalIine, or a temperature of the glass transition temperature-200°C or more and the glass transition temperature-1 0°C or less in the case where the thermoplastic resin is amorphous. 4. The method according to any one of claims 1 to 3, wherein in the prepreg arranging step, the prepreg is arranged such that a total area charge ratio represented by equation (4) is 30% to 100%: total area charge ratio (%)=100x[total base material area (mm2)/total mold cavity m (4) wherein, in equation (4), a total base material area represents an area obtained by subtracting area of layered or overlapping portions from projection area of dl the horizo11My spread prepreg, and a total mold cavity area represents a total areas of mold cavity surfaces. The method according to any one of cfaims 1 to 4, wherein in the prepreg arranging step, ends of a plurality of the prepreg are overlapped. 6. The method according to any one of claims 1 to 5, wherein the average fiber length of the reinforcing fibers is f 0 mm to 30 mm. 7. The method according to any one of claims 1 to 6, wherein the mold has an end clearance of 0.01 mm to 0.1 mm, and the mold is capable of being sealed. 8. The method according to my one of claims 1 to 7, wherein a void hction of the prepreg is 0% to 30%. 9. The method according to any one of claims I to 8, wherein in molding the prepreg, a pressure for pressurizing the prepreg is 3 MPa to 100 MPa. 10. A shaped product obtained by the method according to any one of claims 1 to 9, wherein a ratio (E6) obtained by dividing a larger tensiIe modulus by a smaller tensile modulus among tensile modulus in an arbitrary direction and a direction perpendicular thereto is 1.0 to 1.3.