To obtain a diffuser unit having an internal wind path to which a purifying function can be added selectively depending on the clean level required for a room by disposing a photocatalyst carrier for purifying the air flow to be diffused in the internal wind path.

A duct 4 for conducting air flow from an air conditioner body 2 is branched into two, for example, on the downstream side and each branch is coupled, at the end thereof, with a diffuser unit 3, 9 facing each room R1, R2. Each diffuser unit 3, 9 has an inner wind path being coupled with the air conditioner body 2 through a duct 4 and a diffuser 14 is arranged at the end of the wind path while facing the inside of the room. A photocatalyst carrier 32 is disposed in the wind path of the diffuser unit 3 facing a room R1 to be purified in order to purify the air flow being diffused. The photocatalyst carrier 32 is not disposed in the diffuser unit 9 facing a room R2 not to be purified, e.g. a warehouse.