To safely and efficiently transport a maximum loadage by moving a loading part so that a composed gravity center position falls within a proper range by considering the total weight of the loading part including a live load or the live load.

In a moment when the rear end of a rear crawler mechanism separates from a single step of stairs, a contact point with the crawler mechanism in a step above by a single pitch is denoted by Y. An intersection between a perpendicular A from the contact point Y and a bottom surface of a loading part 5 is denoted by (a). A perpendicular B perpendicular to a traveling device by passing through this intersection (a) becomes the lower limit of a gravity center proper range of the traveling device of the composed center G of gravity. In a condition where the composed center G of gravity comes to the lower side of the stairs than the perpendicular A, the possibility of overturning to the lower side of the stairs is produced. Then, in order to prevent overturning, a loading part 5 is slidingly moved the upper side of the stairs according to a calculated moving distance. As a result, the center G2 of the gravity of a live load moves in the upward direction of the stairs, and as a result, the composed center G of gravity also moves in the upward direction of the stairs, and can be made to fall within a proper range.