In the present invention, liquid absorbent is cooled or heated during off-peak hours of electricity demand to prevent the margin between electricity supply and demand from being tightened. A humidity control apparatus switches an absorbent circuit between a regenerated position in which a regeneration circuit is formed, and a humidity-controlled position in which a humidity control circuit is formed. In the regeneration circuit, during a period during which humidity control operation is stopped, outlet and inlet ends of a regeneration passage communicate with each other, and liquid absorbent circulates within the regeneration passage. In the humidity control circuit, during the humidity control operation, a humidity control passage and the regeneration passage communicate with each other, and liquid absorbent circulates between the humidity control passage and the regeneration passage.