To provide a switch mechanism small in size and simple in structure.

A switch plunger 2 is moved by rotation of a cam 4, and the cam 4 is rotated by insertion of an actuator 20. The switching mechanism has a locking pin 15 leaned toward the surface of a switch plunger 2, and a locking arm 19 movable between a locking position and an opening position. The surface of the switch plunger 2 toward which, the locking pin is leaned, has a contour of a tapered ring-shaped shoulder part formed so as to make the locking pin 15 move by the movement of the switch plunger 2 from the second position to the first position. The locking arm 19 located at the locking position prevents the movement of the locking pin 15 by the contour, thereby, the movement of the plunger 2 from the second position to the first position is prevented. The movement of the actuator 20 is prevented unless the locking arm 19 is moved to an unlocking position by a solenoid to which voltage is applied.