In a first process, an electrically conductive thin metal plate 7 is subjected to a press molding process employing a plurality of punches 3 in a primary molding block 1 and a plurality of dies 4 in a secondary molding block 2, so as to form therein a plurality of hollow projections 9 that project from one side of the metal plate 7, and bulges 14 that bulge out in a direction opposite to that of the projections 9, positioned between the projections 9. In a second process, the metal plate 7 on which have been formed the plurality of projections 9 and bulges 14 is subjected to either chemical etching or electrolytic etching, so as to form through holes 17 by corrosively removing thin-walled portions 11 from the tips of the projections 9, and, at the same time, to corrosively form innumerable fine irregularities 18 over the entire surface of the metal plate 7.