A lock-off switch comprises a lock plate rotatably disposed on a slider and having a projection at one side and a hole elongated in the lengthwise direction and a pin secured to the slider and loosely fitted in the elongated hole of the lock plate thereby to hold the lock plate rotatably. In the elongated hole of the lock plate a compression spring stretches between the pin and one end of the elongated hole, thus urging the lock plate toward a switch case. The slider has a stopper engageable with the projection of the lock plate thereby to stop the slider. An urging means, such as a compression spring, is provided at the other side of the slider and urging the projection of the lock plate into engagement with the stopper, thereby to prevent the slider from being pushed. To push the slider, the lock plate is rotated against the urging force of the urging means thereby to release the projection of the lock plate from the stopper.