PURPOSE: To shorten the time to change over from advance to retraction and vice versa and eliminate risk of shortcircuiting surely by reading the advance/ retraction speed out of the memory, in case the electrode is moved with respect to the work to be processed, and DA-converting the output therefrom to place on the control of motor.

CONSTITUTION: A digital speed command value SD is placed out from a control device 102 to be converted into analog voltage by a DA converter 108 for the purpose of controlling the feed motor 105. The electrode EP is put in a feed motion by the feed motor 105. The feedback pulse FP from a pulsecoder 106 is subjected to subtraction and added to the content of an error register 107b, and the current position of the electrode is grasped through following-up. If a shortcircuit is produced during processing to generate a shortcircuiting signal SS, the control device 102 reads the retractive condition out of the memory and the symbol for the retraction speed SD is inverted for outputting. Thus the motor 105 is reversed promptly.