A machining-energy calculating unit accumulates a discharge current value for each discharge position to calculate a machining energy in a certain time period from the present time to the past time. An energy-distribution changing unit determines the presence or absence of imbalance in the energy by obtaining a machining energy distribution in an up-down direction of the machining gap based on the machining energy, and when there is imbalance, the energy-distribution changing unit produces a new open/close pattern in which a machining energy distribution that eliminates the imbalance. Power feeding is then performed based on the new open/close pattern.