PROBLEM TO BE SOLVED: To provide a filter medium for air filters which uses a polyphenol compound as an antiallergenic agent, is balanced in fire retardancy and antiallergenic properties after exposure to water at a high level and also has excellent processability.SOLUTION: In an antiallergenic filter medium, a polyphenol compound, e.g. tannic acid, and a polyurethane resin containing an alicyclic isocyanate, e.g. isophorone diisocyanate or norbornane diisocyanate, in the molecular skeleton are adhered to the surface of a fiber constituting a fiber sheet containing a thermally adhesive fiber.
