PURPOSE: To reduce or eliminate a rattle between unloaded gears meshed with each other by making teeth of an extension part of an elastomer slightly oversized relative to gear teeth to occupy a backlash space.

CONSTITUTION: In order to overcome a rattle of a gear without a torque load, an extension part 21 of an elastomer is fastened to at least one side of a gear 10, teeth 23 of the extension part 21 is made to have the same profile as teeth 11 of a metallic spur gear 10 but be slightly larger than the teeth 11, and the extension part 21 is overlapped with the teeth 11 by a backlash space. Teeth 13 of a gear 12 is engaged with the large teeth 23 of the extension part 21 though leaving the backlash space from the teeth 11 of the gear 10. Therefore, when the gears are subjected to early oscillatory torque, the large teeth 23 of the extension part 21 eases every impact of the backlash space to prevent a rattle oscillation and a rattle of the gears 10, 12.