PURPOSE: To check whether is in redundant operation or not and, when it is not in redundant operation, to inform the operator of its effect by making a load part inform a load capacity calculating part of the kinds of the load mounted actually and the numbers.

CONSTITUTION: A load part 20 reports the kinds of the devices currently connected to the load and the numbers to a load capacity calculating part 33. The load capacity calculating part 33 calculates the current current being required now in the load part 20, using this information, and sends the results to a comparison part 34. The source part 10 sends the kinds of the power units connected now and the number to the power capacity calculation part 32. The power capacity calculating part 32 calculates the current capacity that the power source part 10 can supply now, using these data and the data of a data part 31, and sends the results to a comparison part 34. The comparison part 34 compares the data from the power capacity calculating part 32 with the data from the load capacity calculating part 33, and judges whether the capacity of the power source 10 has enough redundancy.