DESCRIPTION TITLE OF INVENTION: VEHICLE BODY TECHNICAL FIELD [0001] The present invention relates to a vehicle body which has a longitudinal member disposed as aligned in the front-back direction of the vehicle body, and a I widthwise member disposed as aligned in the widthwise direction of the vehicle body. BACKGROUND ART [0002] Vehicle body composed of a unit construction body (monocoque body) is configured by using, as main skeletal components, long longitudinal members such as side sill, roof rail, front floor having floor tunnel part, and slde member, which are disposed as aligned in the front-back direction of the vehicle body; and long widthwlse members such as floor cross member and roof cross member, which are disposed as dligned in the widthwise direction of the vehicle body. The longitudinal member and the widthwise member are generally joined with each other through flanges formed at the longitudinal (axial) ends of the widthwise member, in order to ensure rigidity of the vehicle body and to bear the load. [0003] The widthwise member is applied with load in the I axial direction thereof induced by deformation of the cross-sectional shape of the longitudinal member, and also with torsional moment induced by displacement of the longitudinal member. The widthwise member is, therefore, required to suppress deformation possibly caused by the load applied in the axial direction, and to have a high torsional rigidity which affects driving stability of vehicles. To minimize the amount of deformation of the widthwise member, it is necessary to effectively apply the axial load to the cross section of the widthwise member, and to optimize the cross-sectional shape and joining conditions of the widthwise member. Also for the purpose of elevating the torsional rigidity of the widthwise member, it is again necessary to optimize the cross-sectional shape and joining conditions of the widthwise member, similarly as described above. [0004] For the purpose of suppressing deformation of the widthwise member under axial load, it is preferable to ensure a large cross-sectional area of the widthwise member, and to join the widthwise members with thc longitudinal member at points in the flange as close as possible to the cross-sectional profile. On the other hand, for the purpose of enhancing the torsional rigidity of the widthwise member, it is again preferable to ensure a large cross-sectional area of the widthwise member. However, in contrast to the above-described conditions for suppressing deformation, it is preferable to join the widthwise member wlth the longitudinal member, at points in the flange as apart as possible from the crosssectional profile. In short, while ensuring a large cross-sectional area of the widthwise member, the geometry of flange of the widthwise member and the points of joining are necessarily optimized, taking suppression of deformation and improvement in the torsional rigidity of the widthwise member into consideration. [0005] Now the flange, which is formed at the longitudinal end of the widthwise member and serves as a joint part between the widthwise member and the longitudinal member, is molded by press molding as a result of extensional deformation. Accordingly, all efforts of forming the flange along the ridge part of the I widthwise member will inevitably result in concentration of the extens~onal deformation locally at the edge of the flange. As a consequence, in the process of press forming, the flange would sometimes rupture at the edge thereof, when intended to be long enough in width. It has therefore been a conventional practice to provide a notch d L around the ridge part of the widthwise member, rather than providing the flange. Alternatively, even if the flange is formed along the ridge part of the widthwise member, the flange has been minimized in width in a portion thereof corresponded to the center in the perimeter direction of the ridge part. As a consequence, the widthwlse member has no joining point, typically by spot weldlng, in the flange thereof especially in a portion corresponded to the ridge part. This has been one of the causes of inhibiting suppression of deformation and improvement in torsional rigidity of the widthwise member. [0006] A specific explanation will be given below, referring to the case where the longitudinal member is configured by the side silis and the tunnel part of a front floor panel, and the the widthwise member is configured by the floor cross member. The floor of the vehicle body (simply referred to as "floor", hereinafter) not only primarily takes part in ensuring necessary levels of torsional rigidity and flexural rigidity of the vehicle body during driving, but also takes part in transmission of impact load in case of car crash, and largely affects the weight of vehicle body. The floor is therefore required to satisfy contradictory requirements regarding high rigidity and light weight. A general structure employed by the floor is such as having the front floor panel; and a floor cross member which is joined to the top surface (the surface faced to the cabin) of the front floor panel, and connects the tunnel part which is formed so as to bulge at around the widthwise center of,the front floor panel, and side sill inner panels which are spot-welded to both widthwise edges of the front floor panel. By spot-welding the floor cross member to the front floor panel, the tunnel part, and to the side sill inner panels, the floor structure will be improved in rigidity, and in load transmission performance under impact load. [ 0 0 0 7 ] In the conventional process of spot welding of the floor cross member respectively to the top surface of the front floor panel, the outer surfaces of the side sill inner panels, and to the vertical wall surface of the tunnel part of the front floor panel, it was general to use an outward flange formed, as a welding margin, at both longitudinal ends of the floor cross member. [0008] The floor cross member is a structural component which takes part in improving the rigidity of vehicle body and in absorbing impact load in case of side impact. In recent years, from the viewpoints of weight reduction and improvement in collision safety, a thinner and more strong high tensile strength steel, for example a high tensile strength steel (HTSS) having a tensile strength of 390 MPa or larger, is used as a material for the floor cross member. The high tensile strength steel has, however, suffered from a low design freedom of the floor cross member, due to its poor formability. [0009] More specifically, for the case where thc floor cross member is composed of a high tensile strength steel of 390 MPa or higher, the flange, which is formed at the end of the floor cross member to be serve as the joint part with the side sill inner panels or with the tunnel part, will be affected by a severe stretch flanging at the edge of the curved part, and may rupture in the process of press forming due to poor formability of the floor cross member. The floor cross member has, therefore, had to be compensated for the shortage of the formability typically by provision of a notch, rather than provision of the flange, at around the ridge part, while resigning itself to degradation in the torsional rigidity and load transmission performance. The notch has, however, been concerned about degradation of various performances of the floor cross member, including collision characteristic regarding axial collapse, and torsional rigidity. [OGlG] Regarding this sort of technology, Patent Literature 1 discloses a floor structure directed to suppress deformation of vehicle interior in case of collision, by providing a means for reducing impact deformation strength, such as a notch, at the end of the floor cross member. Patent Literature 2 discloses a floor structure in which the floor cross member is connected to a side sill, by connecting the floor cross member to a side sill reinforcement. Patent Literature 3 discloses a floor structure elevated in the rigidity by welding the floor cross member and the side sill, by spot-welding the upper part of a side sill inner panel and the flange of the floor cross member. Patent Literature 4 discloses a floor structure in which the floor cross member and the side sill are connected, by folding the edge of the side sill inner panel to be connected to the floor cross member. CITATION LIST PATENT LITERATURE [0011] [Patent Literature 11 Specification of Japanese Patent No. 3120635 [Patent Literature 21 Specification of Japanese Patent No. 2996031 [Patent Literature 31 Specification of Japanese Patent No. 3125476 [Patent Literature 41 Japanese Laid-open Patent Publication No. 02-141372 SUMMARY OF INVENTION 1 TECHNICAL PROBLEM [0012] The floor structure disclosed in Patent Literature 1 I has a risk of excessive intrusion, into the cabin, of a deformed part caused by the means for reducing impact deformation, if the impact load is large. The floor structure disclosed in Patent Literature 2 has a fear of complicating the geometry of the side sill inner panel and the floor cross member, and of inducing crack or degradation of dimensional accuracy in the process of press forming originated from a blank plate. The floor structure disclosed in Patent Literature 3 may not only complicate the geometry of the side sill lnner panel and the floor cross member, but may even dlsable the vehicle body from being assembled in some kinds of process of assembling by spot weldlng, possibly needing a vast change in assembly process of vehicle body. The floor structure disclosed in Patent Literature 4 inevitably increases the manufacturing cost, due to I complicated process of forming of the side sill inner panel. [0013] In addition, although not clearly stated, the floor I cross members in the floor structures disclosed in Patent Literatures 1 to 4, filed in 1988 to 1994, are products of the era wherein the high tensile strength steel was not so popularly used. From this point of view, all products are considered to be made of common steel sheet having a tensile strength of 300 to 340 MPa or around, rather than the high tensile strength steel. Accordingly, even with these inventions, there will be no other choice than providing the flanges at around the ridge part, at both longitudinal ends of the floor cross member made of a high tensile strength steel having a tensile strength of 390 MPa or larger. [0014] It is therefore an object of the present invention to provide a vehicle body which has a longitudinal member, and a widthwise member joined through a flange formed at the axial end thereof to the longitudinal member, which is suppressed in deformation of the widthwise member, and is improved in the torsional rigidity. More specifically, the present invention is directed to provide a vehicle body having, for example, a front floor panel, and a floor cross member which is joined to the top surface of the front floor panel, and connects the tunnel part of the front floor panel and the side sill joined to the front floor panel, having all characteristics of high rigidity, good load transmission performance, and lightness of weight. SOLUTION TO PROBLEM [0015] The present invention is enumerated below. [1] A vehicle body which includes a longitudinal member disposed as aligned in the front-back direction of the vehicle body, and a widthwise member disposed as aligned in the widthwise direction of the vehicle body, the widthwise member having at least a web surface which configures the top surface, a ridge part contiguous to the web surface, and a vertical wall surface contiguous to the ridge part, the widthwise member having a flange formed at the longitudinal end continuously around at least the web surface, the ridge part and the vertical wall surface, and being connected through the flange to the longitudinal member, the flange having a flange width lf,, at the center in the perimeter direction of the curved part thereof, being not smaller than the minimum flange width lf, in the region excluding the center in the perimeter direction of the curved part, and the widthwise member having a tensile strength of 440 MPa or larger. 1 [2] The vehicle body of [I], wherein the widthwise 1 member is a press-molded body having a ditch-like transverse cross-sectional shape. [3] The vehicle body of [I], wherein the ridge part has I .I a radius of curvature R of 8 mm or larger, and the radius j! of curvature R (mm) and the height H (mm) of the transverse cross-sectional shape of the widthwise member satisfy the relational expression (1) below: 0.061R/H10.25 (1) [4] The vehicle body of [I], wherein the flange width lf, at the center in the perimeter direction of the curved part, and the minimum flange width lf, in the region excluding the center in the perimeter direction of the curved part, satisfy the relational expression (2) below: 1f,/1fS21.0 5 ... (2) [5] The vehicle body of [I], wherein the angle formed between the web surface and the vertical wall surface is 80" or larger and 100" or smaller. [6] The vehicle body of [I], wherein the curved part has a joint part to be joined with the longitudinal member. [7] The vehicle body of [6], wherein the joint part falls in a range projected on the flange, the range being determined, when viewed in a transverse cross-section of the widthwise member at around the flange, by a normal llne lnclined by a predetermined angle away from the normal line on the web surface at around the boundary between the web surface and the ridge part, and by a normal line inclined by a predetermined angle away from I the normal line on the vertical wall surface at around the boundary between the vertical wall surface and the ridge part. [8] The vehicle body of [6], wherein the joint part is a I ! spot-welded part. [9] The vehicle body of [I], wherein the flange does not have a minimum thickness in a portion of the curved part, which is corresponded to the center in the perimeter direction of the ridge part. [lo] A vehicle body which includes: a front floor panel which has a tunnel part with a vertical wall, nearly at the center of the widthwise direction, and has flange parts at both widthwise edges; a side sill joined through the flange part to the front floor panel; and a floor cross member which has at least a web surface which configures the top surface, a ridge part contiguous to the web surface, and a vertical wall surface contiguous to the ridge part, and is joined to the top surface of the front floor panel, the floor cross member having the flanges formed at both longitudinal ends continuously around at least the web surface, the ridge part and the vertical wall surface, and being connected through the flanges to the vertical wall and to the side sill, the flange having a flange width lf,, at the center in the perimeter direction of the curved part thereof, being not smaller than the minimum flange width l,, in the region excluding the center in the perimeter direction of the curved part, and the floor cross member having a tensile strength of 440 MPa or larger. [ll] The vehicle body of [lo], wherein the floor cross member is a press-molded body having a ditch-like transverse cross-sectional shape. [12] The vehicle body of [lo], wherein the ridge part has a radius of curvature R of 8 mm or larger, and the I . ~ radius of curvature R (mm) and the height H (mm) of the ' i I transverse cross-sectional shape of the floor cross member satisfy the relational expression (1) below: 0.061R/H<0.25 ... (1) [I31 The vehicle body of [lo], wherein the flange width lf, at the center in the perimeter direction of the curved part, and the minimum flange width lf, in the region excluding the center in the perimeter direction ok the curved part, satisfy the relational expression (2) below: lf,/lf,>l. 05 ... (2) [14] The vehicle body of [lo], wherein the angle formed between the web surface and the vertical wall surface is 80" or larger and 100" or smaller. [15] The vehicle body of [lo], wherein the curved part has a joint part to be joined with the vertical wall or the side sill. [16] The vehicle body of [15], wherein the joint part falls in a range projected on the flange, the range being determined, when viewed in a transverse cross-section of the floor cross member at around the flange, by a normal line inclined by a predetermined angle away from the normal line on the web surface at around the boundary between the web surface and the ridge part, and by a normal line inclined by a predetermined angle away from the normal line on the vertical wall surface at around the boundary between the vertical wall surface and the ridge part. [17] The vehicle body of [15], wherein the joint part is a spot-welded part. [18] The vehicle body of [lo], wherein the flange does not have a minimum thickness in a portion of the curved part, which is corresponded to the center in the perimeter direction of the ridge part. ADVANTAGEOUS EFFECTS OF INVENTION [0017] Accordiny to the present invention, successfully provided is a vehicle body which has a longitudinal member, and a widthwise member joined through a flange formed at the axial end thereof to the longitudinal member, which is suppressed in deformation of the widthwise member, and is improved in the torsional rigidity. According to the present invention, also successfully provided is a vehicle body having, for example, a front floor panel, and a floor cross member which is joined to the top surface of the front floor panel, and connects the tunnel part of the front floor panel and the side sill joined to the front floor panel, being optimized in the geometry of the floor cross member, form and condition of joining between the floor cross member and the side sill or the tunnel part, and thereby having all characteristics of high rigidity, good load transmission performance, and lightness of weight. B R I E F D E S C R I P T I O N OF DRAWINGS [ 0 0 1 8 ] [ F I G . l A ] F I G . 1A is a perspective view partially illustrating a floor structure of a vehicle body according to an embodiment. [ F I G . l B ] F I G . 1 B is a drawing partially illustrating a flange part of a floor cross member of an embodiment. [ F I G . l C ] F I G . 1 C is a drawing partially illustrating a flange part of a conventional floor cross member. [ F I G . 2 A ] F I G . 2 A is a cross-sectional view taken along line 11-11 in F I G . 1 A . [ F I G . 2 B ] F I G . 2 B is a transverse cross-sectional view schematically illustrating an exemplary floor cross member. [ F I G . 3 A ] F I G . 3 A is a drawing illustrating a flange and spot-welded parts of a conventional floor cross member. [ F I G . 3 B ] F I G . 3 B is a drawing illustrating a flange and joint parts of a conventional floor cross member. [ F I G . 3 C ] F I G . 3 C is a drawing illustrating a flange and joint parts of a floor cross member of an embodiment. [ F I G . 3D] F I G . 3D is a drawing illustrating a flange and spot-welded parts of a floor cross member of an embodiment [ F I G . 4A] F I G . 4A is a drawing illustrating straight parts and a curved part o f a flange formed in the floor cross member. [ F I G . 4 B ] F I G . 4 B is a drawing illustrating straight parts and a curved part of a flange formed in the floor cross member. [ F I G . 5 A ] F I G . 5 A is a drawing schematically illustrating a method of forming a floor cross member. [ F I G . 5 B ] F I G . 5 B is a drawing schematically illustrating a method of forming a floor cross member. [ F I G . 6A] F I G . 6 A is a drawing for explaining a conventional blank shape. [ F I G . 6 B ] F I G . 6B is a drawing for explaining a straindistributed blank shape. [ F I G . 7 1 F I G . 7 is a graph illustrating an exemplary relation between position in the curved part of the flange and strain. [ F I G . 8 A ] F I G . 8A is a drawing schematically illustrating an analytical model of the floor cross member. [ F I G . 8 B ] F I G . 8B is a drawing partially illustrating a flange part of the analytical model. [ F I G . 8 C ] F I G . 8 C is a drawing partially illustrating a flange part of the analytical model. [ F I G . 91 F I G . 9 is a graph illustrating relation between energy absorption efficiency under a collision displacement of 5 mm (collision characteristic) and the radius of curvature R of the ridge part. [ F I G . 101 F I G . 10 is a drawing schematically illustrating an analytical model of the floor cross member. [ F I G . 111 F I G . 11 is a graph illustrating rate of increase/decrease of torsional rigidity, with reference to the torsional rigidity under a radius of curvature R of 0 mm, when measured for every ratio of 2R relative to the cross-sectional height H [ F I G . 121 F I G . 12 is a graph illustrating influences of the radius of curvature R of the ridge part exerted on I the torsional rigidity, as compared between presence and I absence of a notch. [ F I G . 131 F I G . 13 is a drawing schematically illustrating an analytical model of the floor cross member. [ F I G . 141 F I G . 14 is a drawing illustrating layouts of the spot-welded points in model A to model G [ F I G . 151 F I G . 15 is a graph illustrating relation between the torsional rigidity, and the number and position of spot-welded points affecting thereon. [ F I G . 161 F I G . 16 is a drawing schematically illustrating an analytical model of the floor cross member. [ F I G . 17Al F I G . 17A is a drawing illustrating layouts of the spot-welded points in model 1 to model 6. [ F I G . 17Bl F I G . 17B is a drawing illustrating layouts of the spot-welded points in model 1 to model 3. [ F I G . 181 F I G . 18 is a drawing illustrating layouts of the spot-welded points in models 2, 7, 8, 9, 10 and 16 [ F I G . 191 F I G . 19 is a drawing illustrating layouts of the spot-welded points in models 2, 11 and 12. [ F I G . 201 F I G . 20 is a graph illustrating the torsional rigidity of models 1 and 3. [ F I G . 211 F I G . 21 is a graph illustrating torsional rigidity of models 3 and 2 [ F I G . 221 F I G . 22 is a graph illustrating torsional rigidity of models 4 and 6. [ F I G . 231 F I G . 23 is a graph illustrating torsional rigidity of models 6 and 5. [ F I G . 241 F I G . 2 4 is a graph collectively illustrating the torsional rigidity of models 2, 3, 7, 8, 9 and 10. [ F I G . 251 F I G . 25 is a graph collectively illustrating absorbed energy of models 2, 3, 7, 8, 9 and 10. [ F I G . 261 F I G . 26 is a graph illustrating torsional rigidity of models 11, 2 and 12. [ F I G . 271 F I G . 27 is a graph illustrating absorbed energy of models 11, 2 and 12. [ F I G . 281 F I G . 28 is a drawing illustrating layouts of the spot-welded points in models 13 to 15. [ F I G . 291 F I G . 29 is a graph illustrating torsional rigidity of models 13 to 15. [ F I G . 301 F I G . 30 is a drawing illustrating layouts of the spot-welded points in models 16 and 17. [ F I G . 311 F I G . 31 1s a graph illustrating torsional rigidity of models 16 and 17. [ F I G . 321 F I G . 32 is a graph illustrating absorbed energy of models 16 and 17. DESCRIPTION OF EMBODIMENTS [0019] An embodiment for carrying out the present invention will be explained below, referring to the attached drawings. This embodiment exemplifies a case where the longitudinal member is configured by the side sill and the tunnel part of the front floor panel, and the widthwise member is configured by the floor cross member. Note, however, that the present invention is not limited thereto, and is also applicable to a case where, for example, the longitudinal member is configured by a roof rail, and the widthwise member is configured by a roof cross member. (00201 FIG. 1A is a perspective view partially illustrating a floor structure la of a vehicle body 1 according to this embodiment. As seen in FIG. lA, the floor structure la of the vehicle body 1 has a front floor panel 2, a side sill 3 as the longitudinal member, and a floor cross member 4 as the widthwise member. [0021] The front floor panel 2 has a tunnel part 2.3 as the longitudinal member, and a flange part 2b. The tunnel part 2a has a vertical wall 2c, and is formed at around the center, in the widthwlse direction of vehlcle body, of the front floor panel 2, so as to bulge to give a ditch-like transverse cross-sectional shape. Inside (below the bottom surface) the tunnel part 2a, a propeller shaft for transmitting englne output to the rear wheels, and various pipings are housed. The flange part 2b is formed upright at each of both widthwise edges of the front floor panel 2. General levels of strength and thickness of the front floor panel 2 will suffice. For example, the tensile strength is typically 300 MPa or around, and the thickness is typically 0.6 to 0.7 mm or around. [0022] The side sill 3 is a long cylindrical body configured by a side sill inner panel 3a and a side sill outer panel 3b. The side sill inner panel 3a and the side sill outer panel 3b are joined to each other typically by spot welding, using flanges respectively formed at the end parts of both components. The side sill inner panel 3a is joined on the outer surface thereof to the flange part 2b of the front floor panel 2, typically by spot welding. General levels of strength and thickness of the side sill inner panel 3a and the side sill outer panel 3b will suffice. For example, the tensile strength is typically 440 to 980 MPa or around, and the thickness is typically 1.0 to 2.0 mm or around. [0023] FIG. 2A is a cross-sectional view taken along line 11-11 in FIG. 1A. As seen in FIG. 1A and FIG. 2A, the floor cross member 4 is a press-molded body composed of high tensile strength steel having a tensile strength of 440 MPa or larger, has a web surface 4a as the top surface, ridge parts 4b, 4b contiguous to web surface 4a, and vertical wall surfaces 4c, 4c contiguous to the ridge parts 4b, 4b, and has a ditch-like transverse crosssectional shape tapered to give nearly a trapezoidal form. The floor cross member 4 also has flanges 4d, 4d which are contiguous to the vertical wall surfaces 4c, 4c and protrude sideward. The floor cross member 4 is joined through the flanges 4d, 4d to the top surface 2d of the front floor panel 2, typically by spot welding. [0024] The floor cross member 4 additionally has flanges 4e. As seen in FIG. lB, the flanges 4e are formed at around both longitudinal ends of the floor cross member 4, continuously along the web surface 4a, the ridge parts 4b, 4b and vertical wall surfaces 4c, 4c. In other words, there is no notch 4f as seen in FIG. lC, which has been indispensable for a conventional floor cross member 4' composed of high tensile strength steel having a tensile strength of 390 MPa or larger. [0025] The floor cross member 4 preferably has a tensile strength of 440 MPa or larger, and more preferably 590 MPa or larger. By the selection, the floor cross member 4 may be thinned, and the vehicle body may be reduced in weight. The floor cross member 4 preferably has a thickness of 1.0 to 2.0 mm for example, more preferably 1.6 mm or smaller, and furthermore preferably 1.4 mm or smaller. [0026] The transverse cross-sectional shape of the floor cross member 4 is not limited thereto, and may be a shape, as typically illustrated in FIG. 2B, with the web surface 4a inclined away from the horizontal line. The angle 9 formed between the web surface 4a and the vertical wall surface 4c is preferably 80" or larger and 100" or smaller. If the angle 9 is smaller than 80°, the torsional rigidity and the collision characteristic will become relatively low. To set the angle formed between the web surface 4a and the vertical wall surface 4c to 80" or larger is one of conditions for maximizing an effect of omission of notch, and for enabling the omission of notch. In thls way, the flanges 4e may be formed by press forming, at both longitudinal ends of the floor cross member 4 composed of high tensile strength steel having a tensile strength of 440 MPa or larger. On the other hand, press forming of the floor cross member 4 becomes difficult if the angle 8 exceeds 100". [0027] The rldge part 4b preferably has a radius of curvature of 8 mm or larger. The radius of curvature R (mm), and the height H (mm) of the ditch-like transverse cross-sectional shape, tapered to give a nearly trapezoidal form, preferably satisfy 0.061R/H10.25, and more preferably 0.06 FIG. 20 is a graph illustrating torsional rigidity of models 1 to 3. FIG. 21 is a graph illustrating torsional rigidity of models 3 and 2. FIG. 22 is a graph illustrating torsional rigidity of models 4 and 6. FIG. 1 23 is a graph illustrating torsional rigidity of models 6 and 5. It was understood from comparison between FIGs. 20 and 22, that a high level of torsional rigidity may be obtained by forming the curved part of the flange without notching. It was understood from comparison between FIGs. 21 and 23, under the same number of spot-welded points, a high level of torsional rigidity may be obtained by disposing the spot-welded points in the curved part of I the flange. If the spot-welded points are disposed outside the curved part of the flange, the torsional rigidity and the collision characteristic will degrade, failing in obtaining desired performances. LO0661 FIG. 24 is a graph collectively illustrating torsional rigidity of models 2, 3, 7, 8, 9, 10 and 3. FIG. 25 is a graph collectively illustrating absorbed energy of models 2, 3, 7, 8, 9, 10 and 3. FIG. 26 is a graph illustrating torsional rigidity of models 2, 11 and 12. FIG. 27 is a graph illustrating absorbed energy of models 2, 11 and 12. 100671 It is understood from graphs of FIGs. 24 and 25 that, for the case where the spot-welded point is disposed in the curved part of the flange, higher levels of torsional rigidity and absorbed energy may be obtained by disposing the spot-welded point at around the center of the flange (a region ranging from 1/10 to 9/10 of the center angle (deg.) of the curved part). [0068] It is understood from the graph of FIG. 26 that, for the case where the spot-welded point is disposed in the curved part of the flange, higher levels of torsional rigidity and absorbed energy may be obtained by disposing the spot-welded point closer to the edge of the flange (a region ranging from 1/2 to 1 of the flange width (mm)). [0069] It is understood from the graph of FIG. 27 that, for the case where the spot-welded point is disposed in the curved part of the flange, higher levels of torsional rigidity and absorbed energy may be obtained by disposing the spot-welded point closer to the rounded rising point of the flange (a region ranging from 0 to 1/2 of the flange width (mm) ) . [0070] In short, it is understood from the graphs of FIGS. 26 and 27 that, for the purpose of balancing high torsional rigidity and large absorbed energy, it is effective to dispose the spot-welded point in a region ranging from 1/4 to 3/4 of the flange width. [0071] FIG. 28 is a drawing illustrating layouts of the spot-welded points in models 13 to 15. As seen in FIG. 28, in all of models 13 to 15, each spot-welded point was disposed the same distance away from the axis of rotation. [0072] FIG. 29 is a graph illustrating the torsional rigidity of models 13 to 15. As seen in FIG. 29, model 13 having the spot-welded point disposed in the curved part of the flange showed the highest torsional rigidity, showing a significant difference. i [Example 21 , . [0073] Using a floor cross member having two spot-welded i points formed in each curved part of the flange, :I influences of the positions of spot welding in the flange exerted on the torsional rigidity and absorbed energy were analyzed. [0074] FIG. 30 is a drawing illustrating layouts of the I spot-welded points in models 16 and 17. I FIG. 31 is a graph illustrating the torsional rigidity of models 16 and 17, and FIG. 32 is a graph illustrating the absorbed energy of models 16 and 17. It is understood from FIG. 31 and FIG. 32 that the torsional rigidity and the collision characteristic are improved by providing the flange around the whole perimeter of the longitudinal end, and by providing a single spot-welded part in each curved part of the flange, and that the torsional rigidity and the collision characteristic are further improved by forming two spotwelded parts in the curved portion of the flange. INDUSTRIAL APPLICABILITY [0075] The present invention is applicable to a vehicle body composed of longitudinal members such as side sill, roof rail, front floor having floor tunnel part, and slde members, which are disposed as aligned in the front-back direction of the vehicle body; and widthwise members such as floor cross member and roof cross member, which are disposed as aligned in the widthwise direction of the vehicle body. CLAIMS [Claim 11 A vehicle body comprlsIng a longitud~nal I I member disposed as aligned in the front-back direction of the vehicle body, and a widthwise member disposed as aligned in the widthwise direction of the vehicle body, the widthwise member having at least a web surface which configures the top surface, a ridge part contiguous to the web surface, and a vertical wall surface contiguous to the ridge part, the widthwise member having a flange formed at the longitudinal end continuously around at least the web surface, the ridge part and the vertical wall surface, and being connected through the flange to the longitudinal member, the flange having a flange width lf,, at the center in the perimeter direction of the curved part thereof, being not smaller than the minimum flange width lf, in the region excluding the center in the perimeter direction of the curved part, and the widthwise member having a tensile strength of 440 MPa or larger. [Claim 21 The vehicle body according to Claim 1, wherein the widthwise member is a press-molded body having a ditch-like transverse cross-sectional shape. [Claim 31 The vehicle body according to Claim 1, wherein the ridge part has a radius of curvature R of 8 mm or larger, and the radius of curvature R (mm) and the height H (mm) of the transverse cross-sectional shape of the widthwise member satisfy the relational expression (1) below: 0.06~R/H~0.25 -.-(I) [Claim 41 The vehicle body according to Claim 1, wherein the flange width lf, at the center in the perimeter direction of the curved part, and the minimum flange width lf, in the region excluding the center in the perimeter direction of the curved part, satisfy the relational expression (2) below: 1fC/1f,21.0 5 0 . . (2) [Claim 51 The vehicle body according to Claim 1, wherein the angle formed between the web surface and the vertical wall surface is 80" or larger and 100" or smaller. [Claim 61 The vehicle body according to Claim 1, wherein the curved part has a joint part to be joined with the longitudinal member. [Claim 71 The vehicle body according to Claim 6, wherein the joint part falls in a range projected on the flange, the range being determined, when viewed in a trai~sverse cross-section of the widthwise member at around the flange, by a normal line inclined by a predetermined angle away from the normal line on the web surface at around the boundary between the web surface and the ridge part, and by a normal line inclined by a predetermined angle away from the normal line on the vertical wall surface at around the boundary between the vertical wall surface and the ridge part. [Claim 81 The vehicle body according to Claim 6, wherein the joint part is a spot-welded part. [Claim 91 The vehicle body according to Claim 1, wherein the flange does not have a minimum thickness in a portion of the curved part, which is corresponded to the center in the perimeter direction of the ridge part. [Claim 101 A vehicle body comprising: a front floor panel which has a tunnel part with a vertical wall, nearly at the center of the widthwise direction, and has flange parts at both widthwise edges; a side sill joined through the flange part to the front floor panel; and a floor cross member which has at least a web surface which configures the top surface, a ridge part contiguous to the web surface, and a vertical wall surface contiguous to the ridge part, and is joined to the top surface of the front floor panel, the floor cross member having the flanges formed at both longitudinal ends continuously around at least the web surface, the ridge part and the vertical wall surface, and being connected through the flanges to the vertical wall and to the slde sill, the flange havlng a flange width lf,, at the center in the perimeter direction of the curved part thereof, being not smaller than the minimum flange width lf, in the reglon excluding the center in the perimeter direction of the curved part, and the floor cross member having a tensile strength of 440 MPa or larger. i [Claim 111 The vehicle body according to Claim 10, I ~ wherein the floor cross member is a press-molded body i having a ditch-like transverse cross-sectional shape. I ' I .! [Claim 121 The vehicle body according to Claim 10, wherein the ridge part hasa radius of curvature R of 8 mm or larger, and the radius of curvature R (mm) and the height H (mm) of the transverse cross-sectional shape of the floor cross member satisfy the relational expression (1) below: 0.061R/H<0.25 ..-(I) [Claim 131 The vehicle body according to Claim 10, wherein the flange width lf, at the center in the perimeter direction of the curved part, and the minimum flange width lf, in the region excluding the center in the perimeter direction of the curved part, satisfy the relational expression (2) below: lf,/lf,>1. 05 - . a (2) [Claim 141 The vehicle body according to Claim 10, wherein the anglr formed between the web surface