PURPOSE: To ventilate the air in a room with heat exchange made simultaneously and purify the supply air by providing a heat exchanger which exchanges heat among a supply air channel, air discharge channel, and air purifying filter provided in the supply air channel.

CONSTITUTION: A supply air channel 1 introduces the outdoor air into a room 3, a discharge air channel 2 discharges the air in the room to the outside, and it is partitioned through a partition wall 4. A heat exchanger 5 is formed through the partition wall 4 in such a fashion as to saddle across both channels 1 and 2. The heat exchanger 5 makes the cool air and hot air that are discharged from the room 3 during room cooling and room heating and the outdoor air which is sucked into the room 3 give and receive heat mutually in order to reduce the heat loss due to ventilaion to the minimum. Because an air purifying filter is provided in the supply air channel it is possible to introduce the outdoor air into the room after purifying it, and because heat exchange is carried out by the heat exchanger between the air in the room that is discharged and the outdoor air that is introduced, the efficiencies of room cooling and room heating do not fall.