This paper presents an advanced parallel two-wheel vehicle that has an underslung vehicle body. In the proposed parallel two-wheel vehicle, since large wheels which its diameter is 1.05[m] are applied, and the battery, the actuators and the controller are placed at the lower position in the vehicle body, the gravity center of vehicle body with a passenger can be assigned at the lower position than the wheel axis. Therefore, the vehicle has a pendular structure that enables the vehicle body with

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... the passenger to always maintain the stable posture, even if the vehicle is in the power-off or control-off condition. A 2-DOF joystick that has operation in pitching and yawing is applied to the proposed vehicle. The elderly or handicapped passenger can operate easily and intuitively the vehicle by this joystick. Moreover, in order to suppress the sway of the vehicle on the pitch axis of the vehicle body while vehicle is driven, the sway suppression control system with an active mass system is proposed in this paper. The control system of the active mass system is designed by a backstepping method. The effectiveness of the proposed pitch sway suppression control system with the active mass system is verified by the experiments using the proposed parallel two-wheel vehicle with an underslung vehicle body.