This paper introduces new attitude control system for solar sail which leverages solar radiation pressure and achieves completely fuel-free and oscillation-free attitude control of flexible spinning solar sail. Novel attitude control device was developed, which is a thin film-type device and can electrically control its optical parameters such as reflectivity to generate unbalance of the solar radiation pressure applied to the edge of the sail. By using this device, minute and continuous control torque can be applied to the sail so that very stable and fuel-free attitude control of large and flexible membrane is realized. The control system was implemented as an optional attitude control system for small solar power sail demonstrator IKAROS. On-orbit attitude control experiments were conducted and the performance of the controller was successfully verified compared with the ground-based analytical performance estimation.