An electric component is mounted on a circuit board, and a pre-foamed heat radiating member is applied on the electric component. The circuit board is inserted into a chassis having a box shape with an opening in one side toward an opposite side of the opening. A thickness of the pre-foamed heat radiating member is less than a distance between a front surface of the electric component and an inner surface of the chassis. Thus, the pre-foamed heat radiating member is not removed by scraping when the circuit board is inserted into the chassis. Then, the pre-foamed heat radiating member is heated and expands until the radiating member reaches the chassis, and a heat radiating path between the electric component and the chassis is provided. Therefore, the heat radiating property of the electric component can be increased.