The invention relates to a device for clamping a workpiece on tool, comprising a ram (3) and a clamp (2), the ram (3) being selectively actuated by a pressurized fluid. The ram comprises a body (1) which, when in use, is secured to the tool and a slide (32) mounted such that it can slide with respect to the body (1). The clamp (2) is hinged with the slide (32) about a pivot axis (A). The body (1) includes a front face (13) beyond which the clamp (2) projects when it is in a clamping position in order to clamp the workpiece. In addition, the clamp (2) also has a release position which it reaches at least partially by pivoting about the pivot axis (A). The slide (32) comprises a piston (321) and a rod (322) that are assembled to one another. The pivot axis (A) is offset by a predetermined distance with respect to the axis of the rod (322) in the direction of the front face (13).