PURPOSE: To prevent deformation at the rear of passenger room even when subjected to shock, by extending the left and right end sections of sub-frame for supporting the rear suspension to the rear of the side sill.

CONSTITUTION: A subframe 1 is extended outwardly in the lateral direction over the chassis frames 4, 5 while its left and right end sections are extended to the rear of rear end of a side sill 7 having closed cross-section and extending in longitudinal direction. Upon rear collision, shocking force inputted from a rear bumper 17 is transmitted to the chassis frames 4, 5 to deform them thus to engage the engaging sections 11a and 10a of a cross member 11 and a defmount bracket 10. The shocking force is transmitted through a def. device 8 to the subframe 1 to displace it forwardly and to collide the left and right end sections of the subframe 1 against the rear end section of highly rigid side sill 7.