PURPOSE: To prevent a floor panel from being deformed at the time of a rear- end collision, enlarge the effective volume of a trunk room and unnecessitate to finish spot knock marks, by fixing rear end parts of side members to a base end part of a bumper stay.

CONSTITUTION: A bumper stay 4A is produced by forming a channel material into an L-shape, and the base end part 4a thereof is placed in the rear end part 2b of a side member 2A, and is spot welded to the side member 2A. A vertically raised tip part 4b of the bumper stay 4A is introduced into the trunk room 9 through a hole 12 in a rear floor panel 3 in the condition of being placed along the inside surface of the rear panel 6. Accordingly, an external impact P at the time of rear-end collision or the like is directly transmitted to the side members 2A through the bumper stay 4A, so that the rear floor panel 3 is not deformed, and a rigid construction sufficiently durable to the external impact P can be obtained.