To uniformly diffuse air supplied in a room, to reduce the occurrence of disturbance of an indoor air flow, and to maintain higher cleanliness by a method wherein an air flow is equalized by resistance against an air flow by an air filter when the air flow passes through the air filter.

An air outlet l is formed by fitting an air filer 4 in an opening part 3 of an air outlet 2. A plane opening part 3a and a side opening part 3b inclining at a given angle are respectively formed in the outlet 2 by a frame material 6 in a state to protrude from a mounting plate 5. In a way that the air outlet is mounted on an air supply port 8 of an air chamber 7 and the air filter 4 is arranged at the opening part 3 of the air outlet 2, the arranging height in a ceiling of the air chamber 7 is decreased to a value lower than that of a conventional type. When, though an air flow is disturbed in the air chamber 7, air through a supply air duct 9 flows through the air filter 4 in the plane opening part 3a and the side opening part 3b, a flow is equalized by resistance and supplied in a given direction and evenly diffused.