A positioning pin and a bolt hole positioned near this pin are provided at a plate-shaped rear-portion attachment face portion of a suspension cross member. A positioning hole having the positioning pin inserted thereinto and a bolt hole positioned near this positioning hole are provided at a tunnel frame on the side of a vehicle. The rear-portion attachment face portion and the tunnel frame are fastened by a bolt inserting into the bolt holes together with a nut. Accordingly, the support rigidity of the suspension cross member during the normal vehicle traveling can be secured and the smooth retreat of the power unit to restrain the collision load from having bad influence on passengers in the vehicle frontal collision can be achieved.