A front cross frame portion (12) is connected to a front cross member (27) provided at a connecting portion (26) between a front floor (6) and a vertical wall portion (7). A rear cross frame portion (13) is fixed to a rear cross member (28) extending along a lower surface side of a rear floor (8) in a vehicle width direction above a differential (16). Thereby, the longitudinal length of a subframe (9) is shortened, the stiffness of the subframe (9) is increased, and the space behind the rear cross frame portion (13) is increased.