Abstract: An electromagnetic clutch includes a worm wheel driven by a drive motor, an armature rotated in operative association with the worm wheel, a rotor rotatable about a same axis as the armature, an electromagnetic coil configured to cause the rotor to generate a magnetic force for causing the rotor and the armature to be moved and pulled into contact with each other along the rotational axis by the magnetic force, and an elastic member interposed between the rotor and the armature, one side of the elastic member being fixed to one of the rotor and the armature, the other side of the elastic member being in slidable contact with the other of the rotor and the armature, the elastic member urging the rotor and the armature in directions away from each other.

Abstract: When an ECU interrupts electric power supplying to an electromagnetic coil with a rotor, a rotor and an armature are controlled at a disconnected state, in which a driving force transmission between a vehicle door and a electric driving power source is interrupted and a manual opening and closing operation of the vehicle door is allowed. When the ECU supplies electric power to the electromagnetic coil, the rotor and the armature are controlled at a connected state, in which the driving force transmission between the vehicle door and the electric driving power source is performed. After the ECU activates the electric driving power source to perform one of an opening operation, and a closing operation, of the vehicle door, the ECU interrupts electric power supplying to the electromagnetic coil and activates the electric driving power source.