PURPOSE: To directly conduct the heat of a high heat generation component like an LSI from the component to a board frame or the like, instead of indirect conduction via a mounting board.

CONSTITUTION: Leads 2 of an electric component 1 are inserted into a mounting board in which a square hole 8 conformable to the package size is formed, so as to be buried. From the opposite surface of the mounting board 5, a box type stiffener 9 or a pedestral type stiffener is directly fixed to the package of the electric component 1, by using thermally conductive adhesive agent. Generated heat is directly conducted to a board frame 11 via each stiffener. Since the generated heat from the electric component 1 is directly conducted to the board frame 1, head conduction efficiency is improved, and temperature rise of the board 5 can be restrained.