To solve the problem where a power system where a failure occurs cannot be detected and the failure cannot be detected until all of a plurality of power supply systems fail since backup is made by another power supply system, when one power supply system fails in a power supply circuit that is subjected to redundant configuration by a plurality of power supply systems.

A voltage comparator for detecting the differential voltage of the output voltage of the DC variable power supply of a plurality of power supply systems, and a control part for judging that the DC variable power supply has failed if the change in the voltage value of the differential voltage of the voltage comparator corresponding to the amount of change cannot be detected by changing the voltage value of the DC variable power supply of one power supply system out of a plurality of power supplies, are provided.