PURPOSE: To prevent impact shocks and collapse of freight from being generated due to an abrupt change in the inclination of a vehicle body at an inclination change point on a road, by a method wherein an auxiliary strut provided with a wheel and operated for securing safety of a truck at an inclination change point is provided at the forward end of a frame for the truck.

CONSTITUTION: When the transport vehicle 1 ascends or descends a slope or stairway 12, if the inclination of the vehicle body is abruptly changed at the inclination change point A, the freight 14 on the vehicle may be collapsed or a floor surface 15 may be damaged. To avoid this trouble, when the vehicle 1 ascends the slope or stairway 12 to come onto the horizontal floor surface 15, the auxiliary strut 17 is depressed by an actuator therefor, the wheel 16 is seated on the flat floor surface 15 to support a front part of the truck 4, and the vehicle is moved while controlling the elevation of the strut 17 so that the truck 4 maintains the angle of inclination of the slope or stairway 12. After the center of gravity of the vehicle 1 passes the inclination change point A, the strut 17 is slowly returned to a stored position, thereby correcting the pose of the vehicle 1 to horizontal running pose. When the vehicle 1 starts descending from the flat ground surface 15, operations reverse to the above are conducted.