The surface refining method is a useful technique to improve the mechanical properties such as the fatigue strength of automobile parts. Double Shot Peening (DSP) method, especially its advanced technique of using extensively small shots (less than φ 100μm) at the secondary peening, can increase hardness and compressive residual stress under the surface of the parts. Although the air direct pressure type Shot Peening (ADP-SP) equipments are used as this method, if DSP becomes possible with the centrifugal force type Shot Peening (CF-SP) equipments, the application of DSP to the big size parts such as Ring Gear for commercial vehicle will be expanded. Therefore, an experiment using two kinds of DSP specimens treated by CF-SP and ADP-SP equipments was conducted, and their surface characteristics and bending fatigue strength were evaluated. As the result, it was found that the surface characteristics and bending fatigue limit of the DSP specimen treated by CF-SP equipments and the ADP-SP equipments are almost the same.