PURPOSE: To enhance an efficiency of cooling/heating by holding comfortableness of a room of a residence, etc.

CONSTITUTION: The air curtain apparatus comprises a blower 4 installed at a ceiling side 1 and having a downward diffuser 2 and a suction port 3 toward an indoor side, and an air duct 8 embedded in a floor 5 and having an upward first opening 6 and second opening 7. The duct 8 is disposed at the opening 6 directly under the diffuser 2. The opening 7 is disposed at an indoor side of the opening 6. Thus, since a curtainlike air flow can be formed between the diffuser 2 and the opening 6, even if an exit/entrance 10 is opened, the air in the room is prevented from being fed outward and the outdoor air is prevented from being fed to the room simultaneously, and invasion of a noxious inset, dusts, etc., into the room can be suppressed. Accordingly, cooling/heating can be efficiently conducted without impairing a feeling of freedom in the room.