PURPOSE: To prevent a lowering of accuracy and circularity of the ground surface due to thermal displacement and friction without increasing the grinding cycle time in a grinding device, which moves backward after the rough grinding.

CONSTITUTION: A control means 130 performs the rough grinding with a grinding wheel 19 till the outer diameter of the surface Wa to be ground achieves the rough grinding finish diameter, and controls a wheel spindle stock 13 so as to move backward to the predetermined back position, and controls the wheel spindle stock 13 so as to move forward for finish grinding of the surface to be ground with the grinding wheel 19, and concludes the grinding when the diameter achieves the finish target diameter. Back position is computed by a back position computing means 170 on the basis of the standard back position, which is computed by a standard back position computing means 150 on the basis of the diameter of the ground surface when the backward movement is started and on the basis of a cause showing change of cutting of the grinding wheel, and the back position correction quantity computed by a correction quantity computing means 16 with the fuzzy inference based on a cause showing passing of the processing time as the input information.