PURPOSE: To reduce the height of a component while increasing the degree of freedom of component selection and to permit free laying of a grounding pattern for a secondary-side electronic component.

CONSTITUTION: The device is constituted in such a way that a single-sided wiring board 11 which shields a soldering-face pattern 4 by an enclosure 1 is arranged and installing between the soldering-face pattern 4 for a power supply wiring board 3 and the enclosure 1, that a grounding pattern 12 is formed on the side of a face opposite to the enclosure 1 of the single-sided wiring board 11 and that a grounding terminal 8 for a secondary-side electronic component 7 mounted on the power supply wiring board 3 is connected to the grounding pattern 12.