To provide an electric motor which includes small loss and heat generation and is easily manufactured.

A slip-ring brush-type power supply device for a rotor includes planetary gear type conductive mechanisms 11, 12. The commutator structure of a DC motor is also constituted. A planetary gear corresponding to a carbon brush of a conventional power supply device for a rotor, which need not interchange the torque with the outside, easily rotates and revolves and is lightened in weight. A commutator-type power supply device for a rotor is constituted by providing a plurality of electrodes in an internal gear 4A.