Abstract: In an actuator, a quick release unit is introduced in a transmission between an activating element and a reversible electric motor for disengaging the activating element (5) from the electric motor and the part of the transmission (6) which is disposed from the motor to the quick release unit. This quick release unit comprises two cylindrical coupling parts (8, 9) provided with axially extending and mutually engaging torque-transferring means (21a, 21b), and where the two coupling parts (8, 9) are mutually axially displaceable and kept in engagement with each other by a spring (25). The two coupling parts may be displaced mutually against the spring (25) by a release mechanism, so that the torque-transferring connection (21a, 21b) between the two coupling parts (8, 9) is interrupted. The quick release unit may be made compact, and especially in connection with a worm wheel (6) with a cylindrical part on the side it may be substantially received in the cylindrical part.