Disclosed is an actuator for a friction engagement device of the type adapted to allow power transmission between two shafts by releasing engagement of the friction engagement device concerned. The actuator comprises a torque/thrust conversion device composed of two elements and adapted to effect and release the engagment of the friction engagement device, a pair of gears respectively connected to the two elements, and a torque generating mechanism gear which is engaged with the pair of gears, the gear ratio between the torque generating mechanism gear and one of the pair of gears being slightly different from that between the torque generating mechanism gear and the other of the pair of gears. In this arrangement, the motor torque is directly converted into the power for effecting and releasing the engagement of the friction engagement device, whereby the control method is simplified and the response to the control signal expedited.