PURPOSE: To protect a control unit from a thermal damage by arranging the control unit in the recess of a thermal insulation container.

CONSTITUTION: A thermal insulation container 3 in which a recess 3a is formed at the upper part is provided in a space positioning at the lower side of the lateral panel 1b of a wheel apron 1. A control unit 4 is arranged inside the recess 3a of the thermal insulation container 3. As a result, the control unit 4 never receives a thermal damage. And by providing the thermal insulation container 3 in the space positioning at the lower side of the lateral panel 1b of the wheel apron 1, the control unit 4 can be arranged in an engine room efficiently. Furthermore, an air cleaner 5 is provided on the lateral panel 1b so as to cover the control unit 4. Consequently, the control unit 4 never receives the influence of the heat invading through the lateral panel 1b.