PURPOSE: To preclude the generation of bad smell by impregnating antifungus agent into a reinforcing sheet superposed on a water vapor permeating film.

CONSTITUTION: Reinforcing sheets Ps1, Ps2, having surface areas wider than the internal area of a feed water tank, are superposed on the surface of a water vapor permeating film P1 consisting of a hydrophobic porous material. The reinforcing sheets Ps1, Ps2 contain anti-fungus agent. The woven cloth or the non-woven cloth of vegitable fibers, chemical fibers, metallic fibers and the like can be used as the material of the reinforcing sheets Ps1, Ps2. Silver zeolite, for example, can be used as the anti-fungus agent. The silver zeolite is prominent in durability, heat resistant property and safe property and is provided with wide anti-fungus effect. Accordingly, the breeding and increase of microbe and the like contained in water passing through the water vapor permeating film P1 can be precluded irreversibly. According to this method, the breeding, increase and the like of microbe, which can be produced in a humidifying element, can be prevented sufficiently and the generation of bad smell can be precluded.