1. An electrical rotating machine, comprising: at least two rotors, each of the rotors having a plurality of permanent magnets along its circumferential direction thereof and arranged coaxially with the other rotor and being driven by means of a compound current supplied to stator coils; and a single stator having a plurality of stator coils through which the compound current is caused to flow, one of the rotors exhibiting a forward saliency characteristic and the other rotor exhibiting a reverse saliency characteristic.