To simplify the construction of equipment by a method wherein a signal expressing the unbalance between output currents between a plurality of inverters in accordance with the fluxes of current balancers.

The output feeders Wi and Wj of the inverters in two systems are let through the annular magnetic cores CR of current balancers BX12-BX23 so as to have the respective current directions opposite to each other. Therefore, if both the currents are balanced, the fluxes are also balanced and the difference between the two currents is zero. If both the currents are not balanced, a flux proportional to the difference between the currents is generated. A voltage (e) proportional to the unbalance flux is induced in a coil CL and outputted as a flux detection signal. As the flux detection signal is proportional to the unbalance value between the currents of the feeder Wi and the feeder Wj, the unbalance between the output currents of the two system inverters is indicated. For instance, the detection signal of a flux detector MX12 shows the current unbalance between feeders W1X and W2X.