In recent years, the practical use of personal mobility of wheeled inverted pendulum mobile robot such as Segway has been advanced. In this paper, this paper focuses on a two-wheeled wheelchair, which is a sitting-type wheeled inverted pendulum personal mobility. In order to improve the traveling performance, the purpose of this paper is to efficiently climb over the steps of the two-wheeled wheelchair. In a situation where the wheelchair climbs over a step, there is a drawback that is a trade-off between stabilizing the posture and applying a torque large enough to climb over the step. In order to solve this drawback, modeling is carried out including the model of the passenger in the situation where the wheelchair climbs over a step. This paper shows a control system to feedback the gravity term applied to the wheel when the wheelchair climbs over a step. By these proposals, the improvement of the traveling performance at the time of climbing over a step is realized. The usefulness of the proposed method is confirmed via the simulation result.