A bumper system, comprising: a bumper stay in which a first tube and a second tube extending in the same direction are connected by a first connection rib provided at least at one end portion and a second connection rib provided at least at the other end portion, wherein the first connection rib has a first stop surface and the second connection rib has a second stop surface; a bumper beam having a first beam hole (23a, 24a) into which one end portion of the first tube is insertable and a second beam hole (23b, 24b) into which one end portion of the second tube is insertable; and a vehicle body plate having a first plate hole into which the other end portion of the first tube is insertable and a second plate hole into which the other end portion of the second tube is insertable, wherein: the bumper system is a system in which the bumper stay and the bumper beam are joined and the bumper stay and the vehicle body plate are joined; the one end portion of the first tube is inserted into the first beam hole (23a, 24a), the other end portion of the first tube is inserted into the first plate hole, the one end portion of the second tube is inserted into the second beam hole (23b, 24b), and the other end portion of the second tube is inserted into the second plate hole; and the bumper stay is joined to both the bumper beam and the vehicle body plate by press-fitting in a state in which the first tube is expanded at both the first beam hole (23a, 24a) and the first plate hole and the second tube is expanded at both the second beam hole (23b, 24b) and the second plate hole; wherein the first connection rib is in contact with the bumper beam through the first stop surface, and the second connection rib is in contact with the vehicle body plate through the second stop surface in the same direction as a direction in which the first connection rib is in contact with the bumper beam in a direction in which the first tube and the second tube extend. a bumper stay in which a first tube and a second tube extending in the same direction are connected by a first connection rib provided at least at one end portion and a second connection rib provided at least at the other end portion, wherein the first connection rib has a first stop surface and the second connection rib has a second stop surface; a bumper beam having a first beam hole (23a, 24a) into which one end portion of the first tube is insertable and a second beam hole (23b, 24b) into which one end portion of the second tube is insertable; and a vehicle body plate having a first plate hole into which the other end portion of the first tube is insertable and a second plate hole into which the other end portion of the second tube is insertable, wherein: the bumper system is a system in which the bumper stay and the bumper beam are joined and the bumper stay and the vehicle body plate are joined; the one end portion of the first tube is inserted into the first beam hole (23a, 24a), the other end portion of the first tube is inserted into the first plate hole, the one end portion of the second tube is inserted into the second beam hole (23b, 24b), and the other end portion of the second tube is inserted into the second plate hole; and the bumper stay is joined to both the bumper beam and the vehicle body plate by press-fitting in a state in which the first tube is expanded at both the first beam hole (23a, 24a) and the first plate hole and the second tube is expanded at both the second beam hole (23b, 24b) and the second plate hole; wherein the first connection rib is in contact with the bumper beam through the first stop surface, and the second connection rib is in contact with the vehicle body plate through the second stop surface in the same direction as a direction in which the first connection rib is in contact with the bumper beam in a direction in which the first tube and the second tube extend. the bumper system is a system in which the bumper stay and the bumper beam are joined and the bumper stay and the vehicle body plate are joined; the one end portion of the first tube is inserted into the first beam hole (23a, 24a), the other end portion of the first tube is inserted into the first plate hole, the one end portion of the second tube is inserted into the second beam hole (23b, 24b), and the other end portion of the second tube is inserted into the second plate hole; and the bumper stay is joined to both the bumper beam and the vehicle body plate by press-fitting in a state in which the first tube is expanded at both the first beam hole (23a, 24a) and the first plate hole and the second tube is expanded at both the second beam hole (23b, 24b) and the second plate hole; wherein the first connection rib is in contact with the bumper beam through the first stop surface, and the second connection rib is in contact with the vehicle body plate through the second stop surface in the same direction as a direction in which the first connection rib is in contact with the bumper beam in a direction in which the first tube and the second tube extend.