An air turbine handpiece comprises a grip portion and a head portion disposed at a tip of the grip portion. In the handpiece, a rotor is disposed in a chamber in the head portion, and a cutting tool is detachably attached to a rotation shaft which is rotated integrally with the rotor. A nozzle opening for injecting air toward a turbine blade portion and an exhaust opening for exhausting the injected air to the outside are opened to the chamber of the head portion. An arc width of the nozzle opening in a circumferential direction is two or more times a height in a direction of a rotation axis of the rotor. The nozzle opening is formed so as to extend in a width direction.
