Actuator adapted to cooperate with a drive of an endothermic engine including power source and a releasable accessory, the actuator including a box-shaped casing, a motorized eccentric group housed inside the casing and including a reduction gearing, an arm cooperating with the eccentric group and supporting a friction wheel adapted to cooperate with the accessory and with the power source, the arm being mobile between an engaged position and a disengaged position of the accessory.