PURPOSE: To greatly increase a grounding area while putting a caterpiller under a car body by constructing the caterpillar in a single-layered structure having approximately the same width as a wheel base.

CONSTITUTION: Shafts 24, 31, 38 to which respective parts are attached are mounted on a frame 16 by means of bearings, and bearing boxes 29, 30 are located at the most rear end portion within an opening 28. Then, they are covered with a caterpillar 15, a sproket 27 and the inside surface sprocket of the caterpillar are engaged with each other, the shaft 31 is advanced by adjusting screws 35, 36, and thus the tension of the caterpillar 15 is made a prescribed value. The rear wheels of a passenger car are removed, an assembled caterpillar device is put under a car body, and a sprocket 12 is tightened by a tie bolt on one side of the car wheel. Successively, a bracket is fixed on the frame 16, and it is tightened by the tie bolt of the car wheel on the other side. Hereby, car travelling on snow is made possible.