A seal material and a washer are fitted on a piping main body of a first piping, a bead portion is inserted into a bead portion insertion hole and the seal material and the washer are inserted into a seal material insertion hole. In this state, a female screw is threaded onto a male screw until a piping side stopper and a nut side stopper are abutted, and the nut member is joined to a piping side tube portion. In a state where the piping side stopper and the nut side stopper are abutted, the seal material is compressed in an axial direction via the washer by the small diameter tube portion and the seal material pressure-contact surface. The seal material is elastically joined to an outer circumferential surface of the piping main body and an inner circumferential surface of the bead portion insertion hole in a radial direction.