According to one embodiment, the A/D conversion unit includes a ΔΣ modulating device which samples the analog electric quantity provided by the electric power system with a predetermined modulation frequency and outputs a bit stream changing over time of single bit obtained by performing ΔΣ modulation, and the digital operation processing unit includes one or more digital filters which inputs the bit stream from the ΔΣ modulating device and of which frequency characteristics differ according to a type of protection control operation, and one or more operation processing elements which perform different kinds of protection control operation processing, based on the bit stream provided by the digital filter.
