To ride across the difference in level with ease, even when a vehicle goes over a road surface in a difference in level shape, and thereby enhance the running performance of the vehicle.

Each hub 20 is provided for the tip end side of each driving shaft 17 for a front axle device 13 by way of a speed reducer and the like, and the hub 20 is integrally provided with each driving wheel 22. The boss part 23B of each rocking bracket 23 is mounted on the outer direcumferential side of each hub 20 in such a way that it can be relatively rotated, and a plurality of track idler rollers 24 are provided for each rocking bracket 23 in such a way that it can be rotated. Furthermore, each carwler 25 is wound around among each driving wheel 22 and respective idler roller 24. Each arm part 16A is integrally formed at the lower surface side of each knuckle 16 forming a part of an axle housing 14, and each cylinder device 26 is interposed between the tip end side of each arm part 16A and each rocking bracket 23 in such a way that it can be telescopic.