To improve surface roughness of a machined surface by obtaining uniform discharge traces through stabilizing and fixing a discharge explosion force during electric discharge machining in machining fluid by controlling a discharge voltage.

In this apparatus, a number of control element circuit units, which can roughly set an output voltage and a limited current value beforehand, are connected in parallel. A discharge command is given to each control element circuit unit so that the control element circuit units are switched in turns from a control element circuit unit of a high output voltage and a low limited current value toward a control element circuit unit of a low output voltage and a high limited current value. Therefore, a voltage wave form corresponding to a discharge state is applied to a gap between a workpiece and a discharge electrode.