In a floor cross member configured by a web surface (4a) as the top surface, a ridge part (4b) contiguous to the web surface (4a), and a vertical wall surface (4c) contiguous to the ridge part (4b), having a tensile strength of 440 MPa or larger, flanges (4e) are formed at both longitudinal ends continuously around at least the web surface (4a), the ridge part (4b) and the vertical wall surface (4c), and the floor cross member (4) is connected through the flanges (4e) to a tunnel part (2a) and to a side sill (3). The flange (4e) has a flange width lfc, at the center in the perimeter direction of the curved part (4e-2), not smaller than the minimum flange width lfs of the curved part (4e-2). Accordingly, a vehicle body, which is suppressed in deformation of the floor cross member (4) and improved in the torsional rigidity, is successfully provided.