A projection portion projecting in the same direction as an offset portion is provided between a welding-spot portion and a joining portion joined to a rear side member in a lower back panel. Accordingly, when a tensile force directed outwardly in the vehicle width direction is applied to the lower back panel, the projection portion is extended by the tensile force thus applied and is displaced toward the opposite side of the projecting direction of the projection portion, that is, toward the opposite side of the offset direction. Hereby, a stress applied to the welding-spot portion in an inclined wall portion can be reduced. This makes it possible to restrain weight and cost and to also restrain stresses applied to the welding-spot portion from the lower back panel and a rear floor pan when a load is input from a towing hitch member.