A top cover (17) is provided at an upper position of a supporting structure (12) of heat exchange device (11), and an upper opening (20C) is configured to be provided in a detachable type cover (20) for constituting this top cover (17) at a position corresponding to a clearance (16) between a radiator (13) and an intercooler (15) which overlap in the flowing direction (A) of cooling air. Accordingly, when a cooling fan (7B) is rotatively driven, the upper opening (20C) allows cool cooling air to flow into the supporting structure (12) and to be supplied to the radiator (13) through the clearance (16) between the radiator (13) and the intercooler (15). As a result, only the radiator (13) which overlaps with the intercooler (15) can be efficiently cooled by the cool cooling air from the upper opening (20C).