An electric rotating machine includes a power transmission mechanism and an armature. The power transmission mechanism is equipped with a first, a second, and a third rotor. The first rotor includes n soft-magnetic members. The second rotor includes k soft-magnetic members. Note that n and k are an integer more than one. The third rotor is made up of magnets whose number of pole pairs is m where m is an integer more than or equal to one. The armature faces the third rotor. The first, second, and third rotors are arranged so as to establish a magnetic coupling among them. The soft-magnetic members of the first and second rotors and the magnets of the third rotor meet a relation of 2m=|k±n|. This arrangement is capable of achieving the transmission of power regardless of electric energization of the armature.