PURPOSE: To make it possible to modify the tooth profiles and traces of gears simply particularly readily in the case of small gears, by rotating a drive gear holding an emery cloth between engaged tooth faces of the drive gear and the gear to be modified.

CONSTITUTION: An emery cloth 3 uniformly coated with minute abrasive particles with adhesive material and the like is inserted between the engaged tooth faces of a gear 1 to be modified and a drive gear 2. The drive gear 2 is rotated in the state that the polishing surface of the emery cloth 3 is brought in contact with the tooth faces to be modified. Since each tooth face of the gears does rolling motion sliding from the tooth tip to the tooth base, by means of this constitution, each tooth face to be modified is polished with the emery cloth 3. Thus, small gears also can be modified simply and readily.