PURPOSE: To substantially reduce a set-up time for improving productivity by selectively providing a fixed reference block and movable phase block according to the transfer reference surface of a workpiece on the front surface of a chuck body provided radially with a plurality of movable jaw bodies.

CONSTITUTION: When a workpiece 2 having a phase reference surface 2a on the left side position is worked, a fixed reference block 5 and movable phase block 6 are mounted respectively on the left side of a chuck body 1 and a movable body 9 at the right side. When the workpiece 2 is sent between the respective chuck bodies 1, both ends of the workpiece 2 are clamped by respective jaw bodies 3 for working the workpiece 2 after the movable phase block 6 is moved leftward to press the phase reference surface 2a of the workpiece 2 against the fixed reference block 5 to determined the phase of the workpiece 2. On the other hand, left and right movable phase blocks 6 are mounted on the workpiece 2 for locating the centripetal phase to press these blocks 6 against the phase reference surface 2a of the workpiece 2 from the left and right directions for locating the workpiece 2.