PURPOSE: To automatically change over spark frequency to one fitted to an intermittent charging cycle, by more lengthening a spark generation cycle or a current predetermined value arrival cycle when a charging mode is changed over to intermittent charging mode.

CONSTITUTION: When the charging mode of DC high voltage to the discharge electrode in an electric precipitator is changed over from a continuous charging mode to an intermittent charging mode, the voltage rising speed of DC high voltage is set so as to obtain a spark generation cycle or a predetermined current value arrival cycle longer than an intermittent charging cycle. By this method, possibility, of an inrush current increasing at the time of intermittent charging or electrode charging voltage rising, is eliminated and stable intermittent charging control is obtained.