To prevent the discharge easiness of an external surge from varying without providing special dust-proofing means, by discharging the surge applied to an outer input terminal conductor to a ground conductor via a resistance filled in holes of the board.

An external surge applied to an outer input terminal pattern 21 of an alumina multilayered board 11 is quickly discharged to a ground 22 via a resistance 24 filled in vias 23 of the board 11, thereby protecting electronic components 28 provided on the board 11 from the external surge. The resistance 24 filled in the vias 23 of the board 11 prevents the water content or moisture from depositing to the resistance 24 surface, thereby preventing the discharge easiness of the external surge from varying and eliminating the need of providing special dust-proofing means.