To make the current balance compensating action which is performed for operating inverters in parallel to be always performed in the same state, regardless of the differences between the balance precision and current stability of the inverters although the differences occur due to the output frequencies, frequencies of the drive signals, and DC power supply voltages of the inverters.

In a method for operating inverters in parallel, an arithmetic unit which performs current balance compensation for operating inverters 10 and 20 in parallel is used, and the current balance compensation by means of the arithmetic unit is performed stably, regardless of the output frequencies, frequencies of the drive signals, and DC power supply voltage values of the inverters 10 and 20 by the use of a means which changes the arithmetic constant of the arithmetic unit, in accordance with the output frequencies of the inverters 10 and 20, a means which changes the arithmetic constant in accordance with the frequencies of the drive signals of the inverters 10 and 20, or a means which performs the current balance compensation by means of the arithmetic unit after the ignition pulse width of the drive signals have been controlled so as to compensate a predicted amount of current imbalance caused by the difference between the DC power supplied to the inverters 10 and 20.