PURPOSE: To improve cooling and heating efficiency and save energy consumed for cooling and heating by discharging and/or introducing air in a room optimally at every times in summer and winter.

CONSTITUTION: In summer, a first switching damper 10 is switched into a position whereat a first duct 6 is connected to a second duct 7. By the driving of a fan, comparatively warm air positioned in the upper part of rooms 1, 2 is sucked out of air discharging openings 3, 4 and is discharged into outside air through the second duct 7. In winter, the first switching damper 10 is switched into a position whereat the first duct 6 is connected to a third duct 8. When the fan is driven, comparatively warm air positioned in the upper part of the rooms 1, 2 is sucked out of the air discharging ports 3, 4 once, then, is sent into the rooms 1, 2 again through a suction opening 15 provided at the lower position of the rooms 1, 2 through the third duct 8.