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