A movable iron core unit includes a movable iron core, which is attracted toward a fixed iron core under excitation of a coil, and a guide member made from a resin material and mounted on an outer circumferential side of the movable iron core. The guide member is constructed from a pair of ring members and connecting members that interconnect the ring members. The ring members and the connecting members are mounted in mounting grooves, which are formed on an outer circumferential surface of the movable iron core, and project only slightly from the outer circumferential surface.