PURPOSE: To enable ventilation to be surely carried out without requiring any special operation if a cooling or a heating operation is being performed by a method wherein air ducts having openings at an upper part and a lower part of a dwelling room are disposed along a wall surface so that air in the air ducts communicates with an outdoor spacing through a heat exchanger disposed at nearly the middle height of the room.

CONSTITUTION: An upper opening 1 is disposed near a ceiling and a lower opening 4 is disposed near a floor. A heat exchanging element 3 is disposed near the middle height of a room and air from the upper air duct 2 and the lower air duct 5 passes only through flow passages in the heat exchanging element, corresponding out of the room. As a heat exchanger, the heat exchanging elements having some thermal conductive spacer plates can be used. In the event that a heat pipe 6 is used as the heat exchanger, this heat pipe 6 is of an upper heating type in which a heat conducting fan 7 at an evaporation part is placed an upper side and a heat conducting fan 8 at a condensing part is placed at a lower part. In addition, the air passing through the heat exchanging elements 3 is also heat exchanged by the heat pipe 6 and heat loss caused by ventilation is further reduced.