PURPOSE: To improve heat balance in a soundproof case and reduce engine noise by introducing exhaust wind which has cooled a working machine, exhaust wind which has cooled an an engine, and exhaust wind from a radiator chamber into a muffler chamber independently of each other by respective exclusive fans.

CONSTITUTION: The inside of a soundproof case 4 is partitioned into an engine room 6 accommodating an engine 1 and a working machine 2, a radiator cham ber 8 accommodating a radiator 11 and a fuel tank 12, and a muffler chamber 7 provided with a cooling wind exhaust port 23. In this case, exhaust wind which has cooled the working machine 2, exhaust wind which has cooled the engine 1, and exhaust wind from the radiator chamber 8 are introduced into the muffler chamber 7 independently of each other by respective exclusive fans 35, 46, 10. Thus, even if a cooling wind intake 26 for a radiator 11 is enlarged, noise produced in the engine 1 and the working machine 2 does not leak from an opening 24, and thus noise can be reduced. Since the exhauste wind which has cooled the working machine 2 is introduced into the muffler chamber 7 independently of the engine room 6, heat balance can be improved.