This paper presents the experimental analysis of power augmentation effects of horizontal axis wind turbine using a tip vane. The flow visualization method is used to analyze the augmentation phenomenon. The flow around a tip vane, tip vortex and flow patterns on the blade surface are visualized. The following results are described. (1) Strength of tip vortex, induced drag and turbulence on the blade tip can be diminished by the tip vane. (2) A tip vane can generate the diffuser effect.