An actuator is disclosed, in particular for a locking unit of an injection compression machine, comprising a hydraulic force translator with two piston units moving relative to each other with different effective areas. The foregoing enclose a pressure chamber together with a cylinder or spacer of the force translator. The smaller piston unit is electrically driven, wherein the axial displacement of the smaller piston unit may be transmitted to the cylinder. The cylinder can be fixed relative to a chassis of the injection compression machine by means of a hydraulic clamping device. According to the invention, the pressure necessary for clamping is delivered by a high-pressure reservoir which may be charged during the displacement of the smaller piston unit.