A control device includes an interpolar average machining voltage detection unit that detects an interpolar average machining voltage between an electrode and a workpiece, an interpolar average machining voltage correction unit that corrects the detected interpolar average machining voltage, a machining speed control unit that calculates a machining speed of the electrode based on the difference between the set voltage, which is set in advance as a target value of the interpolar average machining voltage, and the corrected interpolar average machining voltage, and a drive control device that controls a machining speed of the electrode based on the calculated machining speed. The interpolar average machining voltage correction unit corrects the detected interpolar average machining voltage based on a difference between the calculated machining speed and the set speed, which is set in advance as a target value of the machining speed.