PURPOSE: To change car width and to improve mobility by providing wheels on the front and the rear on the lower side of a side part frame free to revolve and torate as well as providing the side part frame at least on one of upper part frames free to move sideways.

CONSTITUTION: When a wheel motor is actuated, wheels 5 rotate, and a gantry vehicle 1 travels on a road surface G of a tunnel T. Thereafter, when a steer cylinder for directional change is actuated, the wheels move to turn, the vehicle 1 changes its direction and travels sideways 2WS, 4WS, and the vehicle 1 travel tracklessly on the road surface G. Thereafter, the wheels 5 are turned sideways by actuating the steer cylinder, and a side cylinder which is a lateral playing driver 4 is actuated. When a side part frame 3 is laterally moved against an upper part frame 2, car width W is varied and corresponds with inside width of the tunnel T. Additionally in this case, as the wheels 5 are turned sideways, the frame 3 smoothly moves laterally against the road surface G. Consequently, the vehicle 1 can be used even when tunnel width changes and can freely travel.