PURPOSE: To raise an accuracy of a stop position to prevent a circular saw from coming into contact with a work and damaging the work in the positioning of the circular saw to the work by a construction wherein when the lowering of the circular saw is to be stopped, and a lifting force is applied to the circular saw for a short time.

CONSTITUTION: A sliding part 4 is vertically slidably provided on vertical guide bars 2 on a bed 1. The sliding part 4 holding a tenoning circular saw together with a drive source is connected to an air cylinder 8 through a chain 10. A lifting/lowering controller for the sliding part 4 controls the excitation/ nonexcitation of a lifting valve and a lowering valve of the air cylinder 8 by a lifting switch and a lowering switch. The sliding part 4 keeps lowering by keeping the lowering switch depressed. With the detection of the OFF state of the lowering switch, the controller excites a coil for operating the lifting valve to apply a lifting force to the sliding part 4 for a short time counted by a timer. When the timer counts up the time, the controller turns OFF the output of the lifting valve. In this manner, there is no possibility that the circular saw overshoots a stop position.