Abstract: A humidifying apparatus comprising: a pleated functional element comprising a pleated structure and, secured to the pleated structure around a periphery thereof, a reinforcing frame, wherein the pleated structure is comprised of a humidifying membrane and, superimposed on at least one surface thereof, a gas-permeable reinforcing material layer, and a dry-side channel and a wet-side channel which are, respectively, provided on opposite sides of the pleated functional element, wherein each of the dry-side channel and the wet-side channel has at least one pair of a gas-intake and a gas-outlet, the humidifying apparatus having a first pressure-buffering means between the gas-intake and an outside conduit connected thereto and a second pressure-buffering means between the gas-outlet and an outside conduit connected thereto, wherein the humidifying membrane divides the internal space of the pleated functional element into spaces which form a part or whole of the dry-side channel and a part or whole of the wet-side