Abstract: The invention concerns a coupler comprising a cam (211) for locking a tool (100) with the coupler (200), characterized in that the cam (211) comprises for bringing the cam into a locking position, an articulation (213) with a connecting rod (209) itself connected through a bearing (206) to a piston (209) mobile in a bore (203) of the coupler body (200), said piston being subjected to the action of a spring (208), a chamber (220), opening on to a conduit (223), being formed by the piston (205) and the base of the bore (203), and means (215) for being connected to an unlocking object for applying an unlocking torque on the cam.