A housing is molded from a resin material, and a first flange portion of the bobbin forms a fusing protrusion, which is joined and fused with the housing. The housing includes through-holes, which are located on a radially inner side of the fusing protrusion and extends through a portion of the housing in the axial direction. A yoke includes at least one pressure reducing part, which is configured to reduce a pressure exerted to a projection of the bobbin by a flow of the resin material at a time of molding the housing.