To enhance a noise preventive effect by a side cover by adding an outside cover member smaller than a cover main body from its outside to the cover main body fixed to a car body frame so as to be mountable-demountable.

A half or more of the surface area of a cover main body 76a of a side cover 76 is covered with an outside cover member 76b, and since a part is formed as an inside-outside double wall structure, outward transmission of an intake air noise of an air cleaner 59 arranged inside the side cover 76 is effectively prevented. An outside surface of the outside cover member 76b is projected to the outside of a car body more than an outside surface of the cover main body 76a, and even if the outside surface of the side cover 76 is damaged, the outside cover member 76b on which inexpensive painting is performed is replaced, and the cover main body 76a on which large and expensive plating processing is performed may not be replaced.