The present invention is provided with: an insulation holder formed of a thermoplastic resin material and having a first opening; a wire connection ring formed of a thermoplastic resin material and having a second opening; and a joining component inserted astride in the first opening and the second opening, the joining component being formed of a metal material having a higher melting point than those of the thermoplastic resin materials, the joining component having a higher stiffness than those of the insulation holder and the wire connection ring, wherein a welded part is formed by welding in at least a part of an area where each of the insulation holder and the wire connection ring has contact with the joining component.