This paper describes the design of control system for two-leg-wheeled inverted pendulum vehicle called "Personal Mobility Robot (PMR)". PMR has two wheels with swing-arm and seat slider which enables to maintain horizontal posture not only sagittal plane but also lateral plane. Though, these additional mechanisms produce complex three-dimensional effect which may reduce controllability of motion. To realize stability and controllability, the three dimensional physical model of PMR is analyzed and the unity controller is designed. The effect of the control is demonstrated through the experiments in the three-dimensional simulation. As the result, the improvement of stability using additional mechanisms is confirmed by simulation.