In a main magnetic circuit, first pulling force generated based on a first component of the magnetic flux flowing through the main magnetic path pulls a movable core in a reciprocation direction of the movable core. The first pulling force increases with a reduction of a dimension of the gap. In an auxiliary magnetic circuit, second pulling force generated based on the second component of the magnetic flux flowing through the auxiliary magnetic path pulls the movable core in the reciprocation direction of the movable core. In the auxiliary magnetic circuit, the second pulling force with the dimension of the gap being within a first range is changed to be higher than the second pulling force with the dimension of the gap being within a second range, the second range being smaller than the first range.