PURPOSE: To prevent the premature damage of a belt cover fitting part and the generation of noise due to the interference between the belt cover and a fender by fastening a fitting seat of a fender upper face part and the lower face part, along the fender, of the belt cover by a bolt.

CONSTITUTION: A fender 2 with a fastening part 25 for fastening a bolt is provided along a travel wheel 1, and a fitting seat 3, protruding upward, with a longitudinal slotted hole, is provided at the upper face part of the fender 2. A bolt cover 6 for covering a belt transmission mechanism 5 for performing transmission to a travel transmission mechanism in a transmission case 15 is further provided, and the lower face, along the fender 2, of the belt cover 6 and the fixture 3 of the fender 2 are fastened by a bolt. The fender 2 is thereby bolt-fastened to the fixture 23 of a frame 17 and the bolt-fastening part 24 of the transmission case 15 so as to be supported, and the fitting seat 3 of the fender 2 and the lower face part of the belt cover 6 are fastened by a bolt so as to be supported mutually.