PURPOSE: To stabilize the quality of work by performing tight cutting with excellent sharpness after dressing and trueing of grinding wheel while performing additional cutting if it will not reach to the fixed position even upon elapse of predetermined time after spark-out.

CONSTITUTION: If it will never reach to the spark-out fixed dimensional position 4P even upon elapse of predetermined time, in the spark-out grinding after tight-feed fixed dimension cutting of wheel table under excellent sharpness of grinding wheel immediately after correction of grinding wheel, the wheel table is cut again with the tight-feed cutting speed or slower speed to produce a signal indicating arrival to the fixed dimensional position 4P reliably. Consequently, cutting miss will never occur to achieve high machining accuracy of work irrespectively of the sharpness of the grinding wheel resulting in stable quality.