PURPOSE: To easily mount a crawler belt type travelling device on a four-wheel vehicle on the market so as to facilitate the running on snow and others by pivoting rotary shafts on both sides of left and right of a frame, and coupling these rotary shafts with a driving wheel through a power transmission mechanism.

CONSTITUTION: While a driven sprocket 12 is pivoted on the front of a frame 11, a driven sprocket (driving wheel) is pivoted through a transmission case 19 on the rear, and a crawler belt 15 is spread between both sprockets 12 and 13. A wheel supporting mechanism 22, on which to place the front wheel 2 of a four-wheel vehicle 1 on the market and which includes a turn table, is provided at the front of the frame 11. Moreover, rotary drums 41 and 44 to make front and rear two rotary shafts are pivoted on the inner side face of the transmission case 19, and a rear wheel 33 is placed extending over both rotary drums 41 and 44. And the rotary drums 41 and 44 are rotated by the rotation of the rear wheel 3 by an engine mounted on the car, whereby a driving sprocket 13 is rotated through the gear type power transmitting mechanism inside the transmission case 19.