PURPOSE: To enable a device to perform smooth further accurate control, by providing a low speed and a high speed interpolator each driven in a fixed period and its synchronizing 1/n period and using the sum of a pulse, dividing an output into (n) parts, in a low speed side and an output pulse in a high speed side as an interpolator output.

CONSTITUTION: A servo motion, feeding an electrode in a diesinking electric discharge machine performing swivel machining, requires a high speed responsive characteristic such that the electrode 2, for instance, is retractively controlled by detecting a short of a work 1 and the electrode and fed in a normal condition if the electrode restores its condition of the short, and the servo motion, being necessary for decreasing its period of calculation, performs a high speed arithmetic operation in every short period by using sub CPU of a high speed interpolator, promptly and accurately operating a servo motion control. while a swivel motion control or a jog feed and a quick feed or the like, using the main CPU of a low speed interpolator 6 and executing an arithmetic operation in each normal period, can be smoothlyexecuted with no influence to the servo motion control.