A humidity control apparatus is provided with two adsorbing elements. The humidity control apparatus alternately repeats a first operation for dehumidifying air in the first adsorbing element while regenerating the second adsorbing element and a second operation for dehumidifying air in the second adsorbing element while regenerating the first adsorbing element. The second air taken into the humidity control apparatus is formed of a mixture of room air and outside air. In the humidity control apparatus, a mixture ratio between the room air and the outside air in the second air is variable.