The Savonius rotor with two semicylindrical blades is known as a dragtype wind turbine of vertical axis operation. The visualization of the flow fields around the Savonius rotor blades were observed by the tracer method using aluminum powder suspended in the water stream. The flow visualization was carried out for the absolute and relative flows with rigid and rotation camera devices.In the case of stationary rotor, the effect of flow through the overlapping section decreases of a minus torque acting on the returning blade. The torque and power performances of rotating rotor were considerably improved by Coanda-like flow on the convex side of the advancing blade.