PURPOSE: To make it possible to enhance the machining accuracy, by spraying grinding oil onto the attaching surface of a workpiece and a table with the use of an auxiliary nozzle in addition of spraying of grinding oil onto the outer surface of the workpiece by use of a nozzle attached to a grinding head.

CONSTITUTION: When a first grinding head 1 is operated, a solenoid valve 29 is opened to allow grinding oil 17 to be jetted from a nozzle 2 while the temperature of the nozzle 2 is detected by a sensor 3 and is delivered to a control device 14. Similarly, during operation of a second grinding head 6, a solenoid valve 30 is opened to allow grinding oil 17 to be jetted from a nozzle 4 while the temperature of the nozzle 4 is detected by a sensor 5 and is delivered to the control device 14. Further, during operation of a table 11 solenoid valves 31 are opened to allow grinding oil 17 to be jetted from nozzles 9 while the temperatures of the nozzles 9 are detected by sensors 10 and are delivered to the control device 14. The control device 14 computes differences between the delivered temperatures and a temperature delivered from a grinding oil temperature sensor 20, and controls the temperature of the grinding oil 17 by means of a heat-exchanger 15, thereby it is possible to minimize variations in the temperature of the table 11 and a workpiece 18.