PURPOSE: To stabilize the working face of a grinding wheel and the grinding characteristic by setting the rocking center on the center line of the diamond of a rotary diamond dresser, and relatively feeding the dresser and the grinding wheel in the width direction of the grinding wheel in dressing the CBN grinding wheel.

CONSTITUTION: The center of the diamond 25 of a rotary diamond dresser 16 and the rotating center P of a rocking arm 3 are nearly matched with an adjusting bolt 12 in advance. The rotary diamond dresser 16 is rotated by a motor 19, and the rocking arm 3 is rocked around the rocking center P by a motor 7 via a rotary disk 6 and a pin 8. The dresser 16 is also rocked, and the grinding wheel 24 is fed in the width direction into contact with the dresser 16 to be ground for dressing. The distance between the tip of the diamond 25 and the rocking center P is set to the diameter of the diamond 25 or slightly larger than that.