Abstract: A rear underbody which forms a rear-under section of a vehicle body is provided with a pair of rear floor side members disposed along a longitudinal direction of the vehicle body in respective vicinities of both end portions of the rear underbody in a transverse direction of the vehicle body. The pair of rear floor side members each forms an enclosed cross-sectional configuration which extends in the longitudinal direction of the vehicle body. A cross member which extends substantially straight in the transverse direction of the vehicle body is disposed apart from and under a rear floor pan between the pair of rear floor side members at respective substantially central portions of a pair of rear wheel house inners. Both end portions, in the transverse direction of the vehicle body, of the cross member are respectively welded to an inner surface of the inside wall portion, in the transverse direction of the vehicle body, of the rear floor side member.