To effectively prevent noise from leaking from an opening for ventilation to the outside without the risk of deteriorating maintenability such as cleaning in the heat exchanger.

A noise-eliminating duct 20 is formed by providing a lattice- shaped partition 23 for a duct body 21 to form a plurality of ventilation passages 22 and by fitting a sound-absorbing material 24 onto the inside surface of the duct body 21 and the partition 23. The noise-eliminating duct 20 is arranged between an oil cooler 12 and an opening and closing door 14. A guide rail 26 is mounted on a post 25 erected on a frame of an upper turning body. A slider 27 engages with the guide rail 26. The outer surface side of one side surface in the duct body 21 of the noise-eliminating duct 20 is fixed on the side of the slider 27 through the medium of a hinge 28. The device is movable in the direction close to and apart from the oil cooler 12 along the guide rail 26 by the slider 27. In addition, the noise-eliminating duct 20 can be horizontally rotated around a part in which the hinge 28 is provided to the slider 27.