An actuator, especially for seat adjusting devices with at least one electrical engine having subordinated reduction gear and a disconnecting device for manual operation. The generic actuator is provided with a disconnecting device that can be used in all operating processes in a large number of different applications and that guarantees reliable functioning of the disconnecting device without being over-dimensioned and thus uneconomical. The disconnecting device has a coupling insertion spring which determines the release force of the disconnecting device and a reset spring is provided which resets an actuating device.