The present invention comprises: a high-frequency power supply; an antenna group having a plurality of antennas connected to the high-frequency power supply; a plurality of reactance variable elements connected to the feeding sides and the grounding sides of the plurality of antennas; a current detection mechanism which detects the current flowing through the feeding sides and the ground sides of the plurality of antennas; a uniformity calculation unit which calculates the uniformity index value of the current flowing through the plurality of antennas, on the basis of the current value detected by the current detection mechanism; and a reactance changing unit which sequentially changes the reactance of the plurality of reactance variable elements such that the uniformity index value calculated by the uniformity calculation unit approaches a predetermined set value.