Savonius wind turbines are utilized in urban area subject to high turbulence. Past studies for the turbine were conducted for the turbulence intensity lower than 10%. We conducted a series of wind tunnel experiments at high turbulent intensity over 15%, using the space downstream of a large free jet where isotropic turbulence occurs obeying Kolmogorov’s -5/3 power law. By measuring the free-rotational speed, i.e. idling point of the tip-speed ratio, we found increase of the performance due to contribution of turbulence. This supports that the turbine captures kinetic energy of turbulence that corresponds to the frequency band of the rotational speed. Another experiment we examined is supplying a jet from the edge of the Savonius turbine expecting higher net power generation. By PIV measurement and torque measurement, we confirmed significant improvement of the turbine performance.