Abstract: A chuck comprises a mounting base 11, and a protruding shaft 12 protruding from a center of a front surface of the base and having a tapered surface 13 on the outer peripheral surface thereof. A hole 16 is formed in the protruding shaft and has an opened end surface, and the hole has holding portions 14 and pressure portions 15. The holding portions and the pressure portions are alternately arranged, and the holding portions are situated at a plurality of positions evenly spaced about an inner periphery of the shaft 12, and each of the holding portions has a short radius from the center of hole 16. The pressure portions are situated between the holding portions and have a long radius from the center of hole 16. A rotating cylinder 20 is detachably fitted outside the protruding shaft, and a group of rollers 21 is arranged inside the rotating cylinder that the axis of the group of rollers is aligned along the axis of the rotating cylinder and so that they are supported by appropriate means.