PURPOSE: To decrease the loss of power except a diode for preventing reverse currents, by mounting a detecting circuit for detecting the inversion of the current direction fed to load to a plurality of power source devices for supplying power to the same load.

CONSTITUTION: When power is fed to load 2 from a plurality of power source devices 1-1 ∼ 1-N, reverse current detecting elements 4, the minimum resistances, are inserted to each power source device 1, and the directions of minute voltage generated at the both ends are detected by means of reverse current detectors 5. Thus, these devices operate to ensure that the direction of current flowing through the detecting element 4 is inverted when there happens trouble in either of power source devices 1 and a current flows back to the device from another power source device 1, and the change is detected by means of the reverse current detector 5 and displayed to a display circuit 6. Consequently, the loss of power by a diode for preventing reverse currents is eliminated because the diode is not used, and efficiency can be improved.