The straight-bladed vertical axis wind turbine is one of the promising candidates for next-generation power sources because of its high efficiency, quiet operation and structural simplicity. Fewer wind turbines of this type have been manufactured and used so far compared with other types like the horizontal type. Therefore, further improvement in efficiency is essential in order to promote their widespread use. The purpose of this study is to better understand the influence of the blade profile of the straight-bladed vertical axis wind turbine on flow and aerodynamic performance and to improve wind turbine efficiency. Unsteady two-dimensional flow through a wind turbine with a symmetrical blade profile, the diameter of which was 3 m, was numerically computed with a commercial CFD code and the results were analyzed. A wind turbine with outward-cambered blades was then designed in order to increase the rotational force acting on the blade along with a wind turbine with inward-cambered blades for comparison. The computational results showed that the wind turbine with outward-cambered blades was better in performance than the ones with symmetrical or inward-cambered blades. Experiments using small wind turbine models, the diameter of which was 200 mm, were carried out in order to verify the computational results. The experimental results showed the same tendencies as the computational results in spite of the difference in scale, Reynolds number and blade number. The effects on flow and performance were also analyzed by additional computations performed with the same CFD code.