PURPOSE: To stop the operation of power supply devie, by providing the detector which detects the impedance decrease of the third winding of a saturated reactor and detecting the failure of an arbitrary remote power supply device with the said detector, when the power supply device has the failure in which the output current increases.

CONSTITUTION: If a failure is taken place to a device, e.g., control circuit CONT4 of the 1st power supply device PE1 and abnormal high voltage output is produced, that is, if the output current increases regardless of the current increase in the control circuit 4, the current flowing to windings l1, l2 of the saturated reactor increases, and the AC impedance of the winding l3 being the load to the oscillator OSC10 of the detection circuit DET9 is lowered. Thus, before the output current of the 2nd power supply device PE2 sufficiently decreases, power is much fed to the relay circuit RL11 being one load, the relay circuit RL11 is operated resulting in operating a switch circuit SW3, and the power supply device 1 is stopped.