PURPOSE: To check any drop in holding power due to centrifugal force being produced in each jaw with the rotation of a spindle as well as to prevent the promotion of high speed and variations in rotation from occurring by attaching the jaws holding a work pivotally to a chuck body via a pivot in direction of crossing a radius of the chuck.

CONSTITUTION: A draw sleeve 13 is advanced forward, while a spider 12 and a draw bar 20 are moved forward too, and thereby each jaw is opened outward and a work W is mounted on a work receiver 21. Likewise a draw lever 10 is retracted, and a claw 9 is rocked outward, holding the work W. In addition, the draw sleeve 13 is retracted, and the jaw 19 is turned to the inside around an support pin 26, thereby holding the work W with a jaw lever 19b. In succession, a spindle 6 is rotated and the chuck body 1 is rotated too, while the work W is rotated, thus machining takes place. At this time, since the vicinity of a central point of the jaw 19 is pivoted to a support arm through the support pin 26, any possible drop in holding power due to centrifugal force to be produced in the jaw 19 is suppressed.