PROBLEM TO BE SOLVED: To provide a filter medium, having electret characteristics, high filtration characteristics (high collection efficiency and low pressure loss), and at least one functional characteristics of among anti-allergic, anti-biotic, anti-viral and mold resistance； and to provide a method for producing the same.SOLUTION: The filter medium is prepared by spraying a functional agent to a charged nonwoven fabric having the air permeability of 10-50 cm/cm/sec, under the air flow penetrating the fabric at the flow rate of at least 1 m/min and at most 5 m/min and dried. A thin film layer of the functional agent is dispersedly present between fibers of the outermost surface of at least one side of the nonwoven fabric. Also, the area ratio of the thin film layer of the functional agent in the outermost surface layer of the nonwoven fabric is 10%-50%.【課題】エレクトレット性とともに高い濾材特性（高捕集効率・低圧損）を有し、かつ、抗アレルゲン性、抗菌性、抗ウイルス性およびカビ抵抗性の少なくともいずれか一つの機能特性を有する濾材、およびその製造方法を提供する。【解決手段】通気度が１０～５０ｃｍ３／ｃｍ２／ｓｅｃである電荷保持不織布に、該電荷保持不織布を１ｍ／ｍｉｎ以上５ｍ／ｍｉｎ以下の流速で貫通する気流の存在下で機能薬剤を吹き付けて、乾燥せしめ、電荷保持不織布の少なくとも一方の面の不織布最表層の繊維間に機能薬剤の薄膜層が分散して存在し、かつ、該不織布最表層における前記機能薬剤の薄膜層の面積比率が１０％～５０％である濾材とする。【選択図】図２
