Today, aged population is increasing in the world, especially in developed countries. Handicapped people could not fulfill their own task without difficulties. Therefore, medical and welfare robotics has become important. Power assist wheelchair robot has been effective in this field for many years. But, to a certain extend, there is a setback in development due to presence of caster wheels. Turning, overcoming obstacles and reversing will be easy without casters. Casterless wheelchair and its control on a straight line was presented in author's previous paper. Two wheel wheelchair robot on curved trajectory is proposed in this paper. Balancing of wheelchair body is proposed to achieve by controlling the inverted pendulum mounted on the wheelchair. Control equations of the system are derived using Lagrange equation of motion. Body controller is designed combining pendulum controller and wheel controller. Disturbance observer is used to cancel disturbance effects. Simulation was carried out to prove the applicability of the proposed system.