High-solidity straight-bladed vertical axis wind turbines are a promising type of vertical axis wind turbine, but their power efficiency is relatively low because of continuous variation in their wind attack angle. Blade pitch control techniques are therefore suggested to enhance their power generation. This study first develops an optimal blade pitch function based on optimal blade pitch angles obtained by using a hybrid double-disk multiple stream-tube model. A novel blade pitch control device is then designed and manufactured to implement the developed optimal blade pitch function for a high-solidity straight-bladed vertical axis wind turbine. Wind tunnel tests focusing on the power output of the fixed and variable pitch high-solidity straight-bladed vertical axis wind turbines are finally carried out to verify the feasibility and efficiency of the developed optimal blade pitch function and control device. The test results show that the maximum power coefficient could be significantly increased by 78% with the developed optimal blade pitch function, thus demonstrating that the blade pitch control device developed in this study is feasible, functional, and effective.