To make an installation space exclusive to an exhaust pipe line unnecessary, to form the exhaust pipe line in large size by a simple structure and to obtain a high sound-absorbing effect.

A car body frame 15 supporting a wheel is composed of a pair of longitudinally long left-right tubular side frames 16 and a tubular intermediate frame 17 connecting the intermediate sections of the side frames 16. A blower 11 for sucking dust is installed onto the intermediate frame 17, and a nozzle for the blower is inserted into the intermediate frame 17. Communicating holes 30 are formed to the connecting sections of the intermediate frame 17 and the side frames 16, and exhaust ports 32 are formed at the rear end sections of the side frames 16. Throttle plates 33 are fixed into the side frames 16 in front from the exhaust ports 32, and sound absorbing materials 34 are stuck on the internal surfaces of the side frames 16 at positions corresponding to the exhaust ports 32. An exhaust pipe line 35 for the blower 11 is formed of the intermediate frame 17 and the latter half sections of the side frames 16.