As well know, a bicycle is a high efficiency vehicle and is suitable for aging society in the future. In the practical use, however, the bicycle is not always stable and the motion stabilization is required for a widespread application. This paper focuses on the instability of the bicycle. There are few researches which realize the control system supporting driver's operation because human Input is regarded as disturbance and make system unstable. This paper realizes the posture control of the electric bicycle which is able to accept human Input. Estimating human Input from motor reaction torque, control system is constructed without force sensor.