The wind turbines with a flanged-diffuser shroud -so called “wind-lens turbine”- are developed as one of high performance wind turbines by Ohya et al. The performances of the conventional wind turbine and the wind-lens turbines – the compact-type and long-type are experimentally and numerically investigated for unsteady winds. Experimental and numerical examples are presented to demonstrate the dependences of the wind velocity frequency on the power coefficients of the wind turbines in the harmonic oscillating velocity wind. Consequently, using the present designed rotor, the wind-lens turbinesshowthe higher performance than the propeller type wind turbinewithout the diffuser in the oscillating velocity wind. Furthermore, the numerical estimation can predict the power coefficients for the fluctuating flows in 94 to 102% of accuracy.