directions three dimensional position associated with a motion in the z axis direction vertical direction three dimensional motion in the profile grinding operation the motion in the z axis direction being influenced by the inclination of the axis of the helical gear 10 and 5 correction values for motions in the x and y axis directions and about the axis c on the horizontal plane three dimensional motions associated with a motion in the z axis direction vertical direction three dimensional motion the correction values correcting tooth profile errors caused by displacement of the tooth profile grinding line of the grinding wheel 118 on the tooth surface of the helical gear 10 due to the influence of the inclination of the axis of the helical gear 10 three dimensional eccentricity correction values meanwhile along with the calculation of the above correction values of the helical gear 10 the control device 121 actuates the motor 113 m to momentarily retreat the column 113 and then causes the touch probe 120 to be located on the other side in the y axis direction of the column 113 that is actuates the motor 116 m to move the touch probe 120 from the one side toward the other side in the y axis direction along the rail 115 a by means of the grinding wheel head 116 and the arm 119 so that the grinding wheel 118 can be located on the center portion in the y axis direction of the column 113 as a result the touch probe 120 is moved to a retreat position and the grinding wheel 118 is located at an operation start position then after.