A projection is provided in a flange of a resin spool, and a concave portion is provided in a yoke in a position facing the projection. The movement of the spool in the radial direction of the spool is restricted by inserting the projection into the concave portion. Because the inner circumferential surface of the concave portion and the outer circumferential surface of the projection are brought into contact, the movement of the spool in the axial direction of the spool is inhibited by frictional resistance at the points of contact.