To quickly disengage a pinion from a ring gear after ignition of an engine by securing smooth movement of an SL1 plunger 36 and an SL2 plunger 47, and to suppress occurrence of arc when a main contact is closed.

A partition member 76 for partitioning a first movable space in which an SL1 plunger 36 can move on an inner periphery of an SL1 coil 35 in an axial direction from a second movable space in which an SL2 plunger 47 can move on an inner periphery of an SL2 coil 46 in an axial direction is arranged between the SL1 plunger 36 and the SL2 plunger 47, and a vent 77 for allowing the first movable space to communicate with the second movable space is opened on a partition bottom part 76a of the partition member 76. Since pressure variation of the first movable space and the second movable space is suppressed when the SL1 plunger 36 and the SL2 plunger 47 are moved, smooth movement of the SL1 plunger 36 and the SL2 plunger 47 can be achieved.