PURPOSE: To smoothly travel even if a track is bent with a simple structure by preventing a vertical line passing through the center of gravity of a vehicle from passing between the rotary center line of driving wheels and the extension line.

CONSTITUTION: When a vehicle is constituted so that a condition of OD>5OE is realized regardless of a loading cargo, this vehicle does not slip down. When driving wheels 1, 2 are mutually inversely rotated in this state, the vehicle smoothly ascends/descends a track 3 without slipping. Since a worm gear is incorporated into a driving mechanism of the driving wheels 1, 2, when driving is stopped, the driving wheels 1, 2 are automatically locked. Since the locked driving wheels have a clamp function in themselves, the vehicle is reliably held in an optional stopping position.