Bearing pieces are formed on both sides of the rear end of a clincher arm which includes a clincher table for bending a staple at the front end thereof. A magazine member to which staples are loaded and a driver arm for driving out a staple fed from the magazine member are pivotally mounted on an axle, which is provided at the rear ends of the bearing pieces. A handle member is rotatably disposed above the driver arm. A rotation supporting shaft of the handle member is provided at a position somewhat closer to the front than the axle of the bearing pieces. A pin, which is provided at a position closer to the front than the rotation supporting shaft of the handle member, is inserted into an elongated hole formed in each side plate of the driver arm.