PURPOSE: A fixture for workpiece is provided to continuously fix a workpiece by using a hydraulic system, even when a hydraulic pressure is released. CONSTITUTION: A fixture for workpiece is comprised of: a hydraulic cylinder(3); a piston rod(1) mounted movably up and down in the hydraulic cylinder; a collet(7) fixed in the hydraulic cylinder placing the piston rod at the center and having a contraction part(7a) with a slot of the longitudinal direction in the bottom; a locking piston(5) formed movably up and down in the hydraulic cylinder, coupling with the collet and shrinking a shrinkage part inside; and the piston rod and the locking piston operated by a hydraulic pressure.
