A bobbin and a magnetic transmitting/receiving stator are positioned by fitting two positioning projections provided for a bobbin flange into two positioning holes formed in a stator flange. The positioning hole has a circular shape and the positioning projection has a flat oval shape which matches a diameter part of the circular shape so that a resin-passing gap is formed between the shapes. Since the resin-passing gap plays the role equivalent to the role of a resin passing hole, the total number of positioning holes and the resin passing holes can be reduced, and magnetic flux passing through the stator flange can be prevented from decreasing. Since a post-forming resin flows through the resin-passing gap in the positioning part, the flow of the post-forming resin can be made uniform in the whole periphery, and occurrence of poor molding can be restricted.