To restrain influence to the surrounding of the noise caused by functioning sound of an engine, a cooling fan, and the like by releasing it upward or downward.

Respective louvers 22 are formed with a trapezoidal cross section and a lower surface 23B and an upper surface 23A of covers 23 vertically facing each other are set to a different inclination. Thus operating sound of an engine, a cooling fan 9 and the like horizontally propagated toward respective louver 22 sides can be released to the outside by changing the direction upward or downward by the surfaces 23A, 23B mutually set to a different inclination, therefore noise caused by the engine, the cooling fan 9 and the like is propagated toward the irregular directions such to the ground and up into the air and noise with respect to the residents in the environment of a working site, workers around the working site and the like can be relieved.