PURPOSE: To suppress an unbalanced current for an unbalanced voltage by employing partly an unbalanced coil induction motor with unbalanced coil while considering an unbalanced voltage at the coil for a load group.

CONSTITUTION: The relationship of the output voltages of phase number converter 16 at a light load time becomes VUW>VVW>VUV, and the number of load motor 20 used at a light load time so as not to flow an unbalanced current for the relationship becomes nW>nV>nU. On the other hand, the relationship of the magnitude of the output voltage of a phase number converter 16 at full load time becomes VUV>VVW>VUW, and the number of the motor 20 used at full load time so as not to flow an unbalanced current becomes nV>nW>nU. In this manner, the unbalanced current for the unbalanced voltage is suppressed.