A two-wheeled wheelchair is a wheelchair without casters. It is underactuated system, and it can be modeled as an inverted pendulum. A two-wheeled wheelchair has improved former problems of a conventional four-wheeled wheelchair such as going over steps. However, two-wheeled wheelchair has unstable mechanism and must be kept stable by stabilizing control to prevent from falling. Passenger will control wheelchair by moving center of gravity, but this makes controlling two-wheeled wheelchair difficult than conventional wheelchair. In this paper, the motor powered backrest is installed to the two-wheeled wheelchair. The backrest moves according to the command input generated from the speed of the wheelchair, and supports human movement while stopping and improves controllability. The validity of the proposed method is confirmed by the experimental results.