To prevent the occurrence of seizure in a sliding portion by securing specified snow lubrication in the sliding portion between a track belt and a guide rail even without any soft snow on a traveling snow surface during the travel-driving of a snowmobile.

A track belt 9 is wound on two rotary wheels 7 and 8 supported on a car body 2, and the lower part of the track belt 9 between the two rotary wheels 7 and 8 is set as a driving portion 14 where a lower surface thereof is moved backward in contact with a traveling snow surface S. A guide rail 17 is provided to be supported by the car body 2 and pressed into contact with the inner surface of the driving portion of the track belt 9. The driving portion 14 is slid backward with respect to the guide rail 17. In front of the sliding part 32 of the track belt 9, snow scratching-up means 34 and 35 are provided for scratching up snow from the traveling snow surface S following the advancing of the car body 2.