Actuator for actuating a valve device comprising an electric drive (14) being operatively engaged to an actuating element (1) of the valve device, the electric drive (14) comprising at least one torque motor (2) which drives a hollow shaft (3) as an internal rotor, that positions a threaded drive (4) having a screw nut (6) and a threaded spindle (5) for converting the rotational movement of the hollow shaft (3) into a translational movement of the threaded spindle (5), and the threaded spindle (5) acts upon the actuating element (1) for displacing the same, wherein the threaded drive (4) comprises an inverted roller screw (4.1), and the screw nut (6) of the inverted roller screw (4.1) houses the threaded spindle (5) as a push rod.