Airflow is introduced into an enclosure through an air inlet in an electronic component unit. The airflow runs toward a first electronic component. The airflow absorbs heat from the first electronic component. The first electronic component is thus sufficiently cooled. A second electronic component is mounted on a printed wiring board at a position remoter from the air inlet than the position of the first electronic component. An air intake opening is formed in the enclosure. The air intake opening is defined at a section of the enclosure opposed to the printed wiring board at least between the first and second electronic components. Airflow is introduced toward the second electronic component through the air intake opening. The second electronic opening is thus sufficiently cooled. In this manner, the first and second electronic components are cooled equally to the utmost.