To reduce the burden of operator by supporting a tube above a dental treatment instrument under using while preventing a patient from being mentally affected, to improve treatment workability by improving operability of dental treatment instrument, and further, to improve versatility by easily fitting a tube supporting device to an existent unit.

This device is connected to the dental treatment instrument whose one terminal is fixed to a surrounding member 5 including a treatment table 4 arranged near a patient chair and another terminal is attachably and detachably locked to the surrounding member 5, and supports a tube 3 of dental treatment instrument dropped to be almost U-shaped downside rather than the surface of the treatment table at the time of using the dental treatment instrument. The device is provided with a fitting part 10 to be attachably and detachably fitted to the surrounding member 5, arm 15 to be provided at the fitting part 10 and to rise up so as to be stretched, a supporting part 30 provided at the arm 15 for supporting the tube 3 so as to move it back and forth in lengthwise direction, and a guide part 35 for regulating the breadthwise movement of tube 30 supported by the supporting part 30.