Measurements of the gear noise and the dynamic load acting on the meshing teeth of the gears with profile modification and without profile modification which are shifted by different amounts of addendum modification were carried out using power-circulating gear test rigs until a surface failure caused by scoring was observed. According to the experimental results of the gear noise and the dynamic load it is clear that the dynamic load acting on the meshing teeth decreases due to profile modification and that the gear noise of the gears with profile modification is lower about 5 dB than that of the gears without tooth profile modification. Further, the sound pressure levels at all the pass frequencies, the mesh frequency and the 2nd harmonic of the mesh frequency of the gears decrease at the incipient stage of scoring.