The handle body includes a handle body, a push knife, a nail magazine seat and a nail abutment seat. The handle body is provided with a push button for controlling the push knife. 

  The handle body is rotatably connected with a cam, and the cam is provided with a hook. The side of the cam is provided with a safety mechanism. When the safety mechanism is in the locked state, the hook is hooked on the push button, and the cam is fixed relative to the handle body; when the safety mechanism is in the unlocked state, the hook releases the push button. 

  When the safety mechanism is locked, the cam is fixed relative to the handle body, and the push button cannot be moved forward, which prevents the push knife from being pushed prematurely when the position of the instrument is not adjusted properly.