A discharge pulse control device cuts off a pulse width of the a discharge pulse being produced in a machining gap when a comparison result of a voltage level comparator indicates abnormal electrical discharge. Upon detection of abnormal electrical discharge based on comparison results of a high-frequency component comparator and the voltage level comparator, a quiescent period control unit constructed from a discharge pulse diagnosis device, a first pulse counter, a second pulse counter, and a quiescent pulse control device performs change setting of the quiescent period at the time of occurrence of abnormal electrical discharge and sends that information to the discharge pulse control device. Subsequently, the discharge pulse control device performs change control of the quiescent period at the time of occurrence of abnormal electrical discharge so that the discharge pulse and the quiescent time are optimally controlled.