PURPOSE: To have automated grinding over a wide range by feeding back the output amount from a torque sensor to a grinder element drive device and a grinder element pressing device as well as the output amount from a grinder element wear sensor to the grinder element drive device, and thereby controlling the grinding force and peripheral circumferential speed of the grinder element certainly.

CONSTITUTION: The number of revolutions of a grinder element 10 is sensed by a chargable revolving speed meter 33 always to be used as speed feedback amount of a DC motor 36 so as to eliminate deviation of the revolving speed caused by resilience of a flexible shaft 31. Rotation of a DC motor 21 is transmitted to a supporting member 25, where it is applied to a grinder element 10 as a pressure. The output amount from a torque sensor 12 for eliminating deviation of torque because of a shaft 31 is used as a servo driver torque limitation command value for the motors 36, 21, and the output amount from the sensor 12 can be used directly to grinder element performance control while grinder element pressure control is being performed. The condition of the peripheral surface of a grinder element 10 is photographed by a camera 34 at all times to sense the changing diameter, which is sent to a controller 15 to serve for making the peripheral speed of grinder element constant.