PURPOSE: To obtain excellent operability and workpiece gripping stability in a workpiece vice for fixing a workpiece to a machine tool being provided with a movable claw at a moving base moving in the longitudinal direction of a slender base.

CONSTITUTION: A workpiece vice is provided with a moving base 8 sliding along a slide guide 2 provided in the longitudinal direction of a slender base 1, and the moving base 8 is provided with a screw rod 19 for screwing a movable claw 28 forward. In such a workpiece vice, the pin hole 14 of a knock pin 13 for fixing the moving base 8 to the base 1 is formed by opposing a semi-circular cross section groove 12, provided at the moving base, to semi-circular cross section grooves 11 provided on the base 1 side, at specified spaces in the moving direction of the moving base. With this structure, the moving base 8 can be fixed to the base 1 by the short knock pin 13, and the spacing of the adjacent vices can be made narrow at the time of disposing vices side by side.