A rivet nut has a through-hole and a target member is assembled with the rivet nut passing therethrough. The rivet nut includes a cylindrical body, a protrusion formed on and protruding from a lower end of the cylindrical body, and a flange formed on and protruding from an upper end of the cylindrical body. The target member is assembled by the flange contacting an upper-end surface of the target member and the protrusion contacting a lower-end surface of the target member.