PURPOSE: To continually finish in fixed accuracy a surface to be machined further in a fixed machining time, by detecting a motor current in an electric motor, which rotates a wheel, and controlling, so that this current always holds a predetermined value, the pressing pressure of the wheel with a value of the motor current being negative feedback controlled.

CONSTITUTION: A cutting speed instruction 1, being compared with a motor current driving a wheel, is input to a pressure controller 2, and its output drives an oil pressure control valve 3. This pressure of oil, operating a wheel spreading cylinder 4 generating pressing force of the wheel to a work, performs honing 5. And a required cutting speed 6 is generated. Here a motor current detecting device 7 detects the motor current to be negative feedback controlled so that the cutting speed 6 may trace a predetermined curve. Consequently, a surface to be machined comes to continually provide fixed finishing accuracy and roughness, while a fixed machining time can be obtained.