An actuator for a four wheel drive transfer mechanism which is laid in a power transmission device and is controlled by an electrical signal sent from a controlling unit comprises a torque generating mechanism which converts electrical energy into a torque, and a torque-thrust conversion mechanism which converts the torque generated by the torque generating mechanism into a thrust force. The thrust force generated from the torque-thrust conversion mechanism is applied to the frictional engaging device to control torque distribution between front and rear vehicle wheels.