To provide a chuck which evenly and accurately moves each jaw in a chuck radial direction to a comparatively large degree while providing a small composition with a small outer dimension in a simple mechanism.

The chuck 1 is provided with a plunger 7 provided in a machine casing 6 such that it can move fore and aft, and a plurality of jaws 8 moved inward by forward movement of the plunger 7. A guide groove 44 wherein a bottom face is a wedge face 46 inclined inward toward the rear and both side faces are guide faces 45, is provided on an outer side of each jaw 8. A guide piece 40 corresponding to the guide groove 44 of the jaw 8 is provided such that an inner face is a wedge face 42 lapping on the wedge face 46 of the guide groove 44, and both side faces are guide faces 41 lapping on the guide faces 45 of the guide groove 44. By forward movement of the plunger 7, the wedge face 42 is moved forward on the wedge face 46, each jaw 8 is moved inward, and a spring 52 carrying out energization such that each jaw 8 is guided outward, is crossed between adjacent jaws 8.