To provide a hydraulic stock vice allowing maintenance work to be performed very easily in a short period of time to maintain expected clamping force to a workpiece.

This hydraulic stock vice comprises: a rotating shaft 44 rotated integrally with a spindle 24 when not clamping the workpiece and rotated relatively to the spindle 24 and relatively moved in an axial direction when clamping the workpiece; a piston member 96 for generating hydraulic pressure by entering a hydraulic chamber 114 of hydraulic booster mechanisms 78, 84, 96; and a pressing member 74 for pressing the piston member 96 when the rotating shaft 44 moves relatively to the spindle 24. The pressing member 74 is provided movably in an axial direction, and regulating means 66, 70 are provided for regulating the movement of the pressing member 74 in an opposite direction to the piston member 96 side.