To provide a workpiece holding device for a machine tool that can detect an advance limit of a piston without fail.

The piston 30 housed in a cylinder 29 is provided with a first advance passage 45, and the cylinder 29 is provided with a second advance passage 46. The second advance passage 46 is coupled to an advance pressure sensor 49 via a pilot control check valve 51. The check valve 51 and an advance pressure passage 43 are connected by a first pilot passage 53, and the check valve 51 is opened in advance. When hydraulic fluid is supplied into an advance pressure chamber 41, the piston 30 advances, and the first advance passage 45 communicates with the second advance passage 46 when the piston 30 moves to the advance limit. Accordingly, pressure acts on the advance pressure sensor 49 from the advance pressure chamber 41 through an advance pilot passage 456 and the opened check valve 51, whereby the advance limit of the piston 30 is detected.