To simplify the constitution and prevent the occurrence of an abnormally high voltage, when interconnecting the regenerative energy of a motor with a commercial system.

AC power via a line 22 from the commercial power system is given for drive to a plurality of motors 23 after being converted into DC by a converter 25 or converted into AC by the first inverter 27. The regenerative energy of the AC from the motor 23 is given to a DC bus 31 from an interconnecting circuit 33 for regenerative energy after being converted into DC by the first inverter 27. The DC of this DC bus 31 is interconnected with the commercial system via the second single inverter 34. The output of a dispersed power source such as a fuel cell 38, a synchronous generator 43, etc. is given to the DC bus 31 via interconnecting circuits 41 and 46.