A motor/generator comprises a stator (2) having plural coils (C1-C14), and plural rotors (3, 4) disposed coaxially with the above-mentioned stator and driven by a compound current. The phase difference between the currents (70, 71) driving the rotors (3, 4) is arranged to be other than 180 degrees. Thereby, the utilization factor of the voltage of the direct current power supply (10) is improved.