When a yoke 11 is inserted into a bobbin hole 20 from the one end of a coil bobbin 13A, 13B until a positioning portion 17 of the first leg 11A, 11B of the yoke 11 is brought into contact with the one end of the coil bobbin 13A, 13B a engaging portion 18 of the first leg 11A, 11B is engaged with the projection 13e of the coil bobbin 13A, 13B within the bobbin hole 20 so that the longitudinal movement of the yoke 11 for the coil bobbin 13A, 13B is limited. Through this limitation, the yoke 11 can be attached to the coil bobbin 13A, 13B.