To restrict the damage of a car at its light collision to the member end part solely, secure a crushing space, and generate a follow-up after the directionality in collision.

A car body substructure is equipped with a fore-and-aft skeleton member 1 installed in the fore-and-aft direction of a car body and leading to the car body end part, an extension member 3 arranged so that one end is butted to the end of the skeleton member 1 in the longitudinal direction, and an end cross member 5 installed across the car width on the side with car body end part, wherein the end cross member 5 is located over the extension member 3, and the skeleton member 1 in the longitudinal direction and end cross member 5 are coupled together by a bracket 11 which transmits the force originating from the vertical direction moment acting between the two members.