PURPOSE: To enable the work increasing the strength of a dedendum, by moving a moving means with its approach to a gear, and equipping a pressurizing means which abuts an abutment member on the dedendum and also pressurizes the dedendum by the abutment member.

CONSTITUTION: First, a gear 1 is installed to a support mechanism 15 with a rotating shaft 10 being supported on a shuck 16 and centering shaft 17. Then, respective moving mechanisms 18 are approached to the gear 1, by actuating respective cylinders 19. The respective pressurizing rollers 21, then, intrudes in the tooth groove of the gear 1, and abuts on dedendum 3. Further, a residual compression stress is imparted to the internal part of the dedendum 3 with the respective dedendum 3 abutted with the pressurizing roller 21 being pressurized, by pressurizing the moving mechanism 18 in the direction approaching to the gear 1 by the cylinder 19. Thus, the fatigue strength of the dedendum 3 can be increased with the residual compression stress being imparted to the internal part by the pressurizing roller 21 on the dedendum 3 of the gear 1, also, with the surface of the dedendum 3 being hardened, etc., by pressurizing.