To prevent potional deviation from occurring due to inclination of a rotary grinding wheel and to grind the flank of a workpiece by the rotary grinding wheel in a constant position.

This grinding method determines a positional deviation amount of a rotary grinding wheel 7 as correction data when the rotary grinding wheel 7 is inclined before a workpiece 5 having a clearance angle is ground. When the workpiece 5 is ground, according to the correction data, the rotary grinding wheel 7 is inclined correspondence to the clearance angle of the workpiece 5 and a surface to be ground, simultaneously, is ground by the grinding wheel after movement in an X-axis direction or in an Y-axis direction is carried out.