PURPOSE: To reduce the load and fatigue of an operator by operating a pinching means with a drive signal to keep the length of a tube from a stationary tool to a hand piece at the desired length.

CONSTITUTION: A hand piece 1 is normally mounted on a stationary tool 3, and a tube 2 connected to its rear end section is fixed to a tube fixing section 33 through the hollow section of the stationary tool 3. A tube holder 4 is fixed to the stationary tool 3 via a bracket 31. The tube holder 4 is a cylindrical insertion body with a hollow section, the tube 2 is inserted into the hollow section, and a disk-shaped pressing plate 41 is provided on the inner face of the hollow section. The pressing plate 41 is pressed toward the peripheral wall of the hollow section by a pressing means 42. When the hand piece 1 is removed from the stationary tool 3 and a detecting switch 46 is operated, electric power is fed from a motor driving power source to operate the motor 42 serving as the pressing means, and the pressing plate 41 is pressed. The pressing plate 41 presses the tube 2, and the tube 2 is pinched and held between the inner periphery of the hollow section and the surface of the pressing plate 41 so that it can not be slid.