When a push lever is brought in contact with a member to be driven, a second trigger stopper slides and a first trigger stopper slides via a second spring. After a third trigger stopper turns ON a push switch 18 according to sliding of the first trigger stopper, the first trigger stopper further slides and a projecting portion and a projecting portion of a trigger are disengaged from each other, so that the trigger is made rotatable. A trigger switch is turned ON according to rotation of the trigger.