PURPOSE: To facilitate sealing processing and improve anti-liquid leak by using two layers or more of two kinds of, namely nonwater containing and water containing materials as impregnation material, and suppressing the permeability of electrolyte.

CONSTITUTION: A laminated impregnation material 6 is formed by piling up non- woven fabric 6B made of polyamide resin on both sides of the filter paper 6A having the main component of wooden pulp. As the non-woven fabric 6B described above, besides polyamide resin, polypropylene non-woven fabric is desirable which melts at 150∼250°C and can be made thinner. After lamination, the peripheral part is pressure-applied by a holder 9 made of teflon, through using a heating head 8 temperature-controlled at 200°C. Resin is melted and impregnated into the filter papre 6B, and the thickness is reduced into 6C, and further water shedding performance is provided with.