PURPOSE: To obtain inexpensively a durable high precision gear, by meshing gears and rotating them while being fed with an abrasive agent, and applying coating whose thickness is equal to a backlash quantity, after a cleaning process at the time of backlash having been increased by a predetermined quantity.

CONSTITUTION: Diamond powder is mixed with lubrication oil, and it is fed to the meshing portion of a gear 1 and a gear 3, and the adaptation rotation of both gears 1, 3 is conducted. At first, there are large sounds, but they become quiet soon, which is an indication of a state in which the best meshing is being conducted. This adaptation rotation is continued further, and when sounds become a little higher, tooth form surfaces are cut excessively as much as thickness D, and circumferential backlash is increased by more than a predetermined quantity, but meshing becomes smooth. The adaptation rotation is stopped in this state, and both gears 1, 3 are cleaned, and coating whose thickness is equal to the thickness D, is uniformly applied to the surfaces of both gears 1, 3. The coating material is selected according to a use condition, and coating is done by means of spattering, chemical vaporization, ion grating or the like.