Focusing on the effect of TI/TL, that represents the characteristics of natural wind, the degree of influence was examined on aerodynamic drag. CD in natural wind was defined as the difference between CD weighted under quasi-steady and CD under low turbulence conditions, and the relationship was verified in the 25% and 100% FKFS SWING wind tunnel and Honda wind tunnel. The physical phenomenon difference between the weighted CD and fluctuating components of CD under natural wind was elucidated, and the concept of CD reduction under natural wind turbulence was clarified.