A projection welding structure including plural projection portions that are provided to an end face at an open side end portion of a reinforcement member flange portion and are disposed at intervals along the length direction of the reinforcement member. The plural projection portions are each abutted and welded to welding projections formed in a surface of a panel frame. Contact between the welding member and the welded member is suppressed at locations other than at the welding projections by such a structure.