PURPOSE: To allow the easy selection of the supply opening for cooling water according to the cutting condition of a tooth by building a valve disk for switching the supply opening for the cooling water in an arm part and providing an operating ring communicating therewith.

CONSTITUTION: A cooling water supplying pipe 43 is connected via a through-hole 35 of the operating ring 31 to a 1st cooling water supplying pipe 55 and is connected via a communicating hole 63, a pipe 45 and a through-hole 37 of the operating ring 31 to a 2nd cooling water pipe 55 when the operating ring 31 is positioned as shown in Fig. relative to a 1st core 28, a 2nd core 29 and a 3rd core 30. The cooling water flows to the cooling water passage of a head part 2 and is blown out of the front end face of a dental bar A. The cooling water is simultaneously blown out of the cooling water nozzle toward the bar A for dental purpose and the tooth. The cooling water is supplied only from the front end face of the dental bar A when partition plates 33, 34 rotate until the plates collide against a recessed part 41d upon rotating of the operating ring 31 in a counterclockwise direction. The cooling water is supplied only from the cooling water nozzle when the partition plates 33, 34 rotate until the plates collide against the recessed part 41d upon rotating of the operating ring 31 in a clockwise direction.