PURPOSE: To suppress the frequency variation of a power system, for the sudden and sharp active power variation of an arc furnace, by suppressing the transmission of the active power load variation from an arch furnace to a power system.

CONSTITUTION: This device is equipped with an arc furnace 3, which receives power from a power system 1, an active power load detector 6 for it, a switch controller, and a plural sets of compensation loads 5 which have plural sets of switches 6 and absorb the received surplus power to the active power load of an arc furnace.