To prevent a vehicle outside plate being damaged at car collision and reduce damage to a car body by surely making underframes collide with each other if by any chance a collision accident should occur to make height difference between underframes of vehicles.

In an underframe connecting a side beam 1 and an end beam, a side beam enforcement member 4 and an end member reinforcement member extending out from the side beam 1 and the end beam upward, or downward, or to both directions are provided, and a joint part of the side beam 1 and the end beam is formed wider upward, or downward, or to both directions than a vehicle center part.