PURPOSE: To use a battery safely in a power controller to be applied to an apparatus using a nickel-hydrogen battery as power supply.

CONSTITUTION: An apparatus is equipped with two classes or more of separate temperature-rise limiting circuits arranged in the apparatus and detecting a temperature rise to interrupt or limit a current, e.g. thermal fuses 4, 4 and thermal protector 13, thermistor 3, power controller 11, FET2 and DC/DC converter 6. Further, when the apparatus is also equipped with two classes or more of separate overcurrent-detecting and limiting circuits detecting overcurrent to interrupt or limit a current, e.g. breaker 1; FET2, current-detecting circuit 15, power controller 11 and DC/DC converter 6; and fuse 5 so that a nickel- hydrogen battery 14 is surely protected by other circuits even if any of the detecting circuits is defective in operation.