In order to increase the operational safety of an actuator (1) including an electric motor (2) and a transmission, preferably a non-self-locking transmission (3), a braking device is provided which allows the controlled, self-actuating displacement, by a retarding brake (5), of an actuating element connected to the actuator (1) via the transmission (3). The actuating element can be held in a fixed position by an additional holding device (6), even if the electric motor (2) fails. The actuator can be used to drive heavy sluice gates, in the event of a power failure, in a controlled free-fall operation at a constant rate of fall, or to hold them in a defined position. The holding device and the retarding brake can be combined in a common housing (11) to form a braking module (12) which can be designed to be used modularly with existing motor actuators and transmissions.