To shorten the length of a dental straight hand piece.

A pair of axially symmetric slits 3a, 3a are formed so as to axially extend in a hollow part formed in the distal end part of a rotary shaft 3. A chuck shaft 1 is inserted in the hollow part of the rotary shaft 3 so as to be axially movable therein, and upon chucking, a chuck shaft pressing unit 7 is pressed in the direction of the arrow. By a spring 4, a cutting bar 2 is clamped. Upon unchucking, a manipulating lever 5 which is rotatably attached to a hand piece body 8 is turned so as to rotate a cam 6 which then presses a collar part 7c of the chuck pressing unit 7 on the side where the spring is arranged, in the direction of the arrow B in order to open the chuck. Since the cam 6 is arranged in parallel with the chuck shaft pressing unit 7, the length of the hand piece body can be shortened by a corresponding degree (which is equal to a moving stroke of the cam).