When an electric appliance unit functions as an electric motor, a rotary shaft is rotated by electric current supplied to the electric appliance unit. When the electric appliance unit functions as a generator, the generator generates electricity as the rotary shaft rotates. A first rotation permitting mechanism is located between the rotor and the rotary shaft to permit the rotor and the rotary shaft to rotate relative to each other. A one-way clutch is located between the rotor and the rotary shaft. The one-way clutch permits the rotary shaft to rotate in one direction relative to the rotor and prevents the rotary shaft from rotating in the other direction relative to the rotor. A second rotation permitting mechanism is located between the housing and the rotor. The second rotation permitting mechanism permits the rotor to rotate relative to the housing. Power transmitted from the external drive source to the rotor is transmitted to the rotary shaft via the one-way clutch. The rotor is supported by the housing with the second rotation permitting mechanism.