A movable core sliding in a guide portion includes a small outer-diameter part, a large outer-diameter part, and a protrusion part. When a magnetic circuit is generated by energizing a coil, a magnetic attractive force inclining with respect to a center axis of the guide portion is generated between the guide portion and the movable core, and moves the movable core towards a stator core. Then, a sliding portion, which is provided over the whole periphery of the small outer-diameter part, and the protrusion part of the movable core are abutted on an inner peripheral surface of the guide portion, a clearance is generated between an outer peripheral surface of parts of the movable core except the protrusion part and the inner peripheral surface of the guide portion. Since the valve member can be opened by a small magnetic attractive force, a coil assembly can be made small.