A walking vehicle has potential capability to be developed to an off-road machine with high mobility and adaptivity by using the coordination control of its multi-degrees of freedom. There have been several discussions on the gait control of a walking vehicle, although few have mentioned the total gait control system and any sub-systems integrated into the total structure. This paper discusses the gait control system based on a quadruped walking vehicle developed by the authors. At first, the premises for the discussion are confirmed. Then, the total structure of the control system, consisting of three levels named A, B and C, is clarified. The control algorithm of each level is studied in detail, particularly the three sub-systems belonging to level B, i.e. gait control in xy coordinates, the same in z coordinate and trajectory control of legs taking account up/down swinging. The control algorithm at level C, which regulates the basic reflex motions, is specifically discussed. Finally, these discussions are verified by walking experiments of a model TITAN III. The joystick control of omnidirectional motions and adaptive locomotion over irregular surfaces are successfully demonstrated.