To prevent a trembling of a grinding processing surface by de- energizing a grinding wheel motor and finish-grinding by maintaining a motive portion from the grinding wheel motor to the grinding wheel in the state that the grinding wheel is rotated by a rotation force due to inertia.

After rough shaving, an X axis servo motor 12 is changed to a speed corresponding to a speed at which a feeding of a grinding wheel 6 becomes a finish feeding. At the same time, a numerical control device 13 controls a grinding wheel motor driving part 14 to de-energize a grinding wheel motor 3. So, the grinding wheel rotates by an inertia. A trembling mark is removed at the time of finish grinding and spark out even if the trembling mark caused by a trembling vibration based on an electromagnetic vibration is generated on a work W at the time of rough grinding by not energizing the grinding wheel motor 3 during finish grinding step. Even in the case where there is a condition that the trembling mark caused by the trembling vibration based on the electromagnetic vibration is generated by energizing the grinding wheel motor 3 at the time of finish grinding, since the grinding wheel motor 3 is de-energized, the trembling vibration is not generated.