PURPOSE: To invariably perform effective sterilization and give no harm to occupants by conveying the air sucked from a base section near the floor face of the wall of a closed room toward a ceiling along the wall, sterilizing it with an air sterilizing means having a ultraviolet source, then blowing it into the room from above.
CONSTITUTION: A ultraviolet air sterilization duct 20 is fitted at the upper section of one wall W of a room R not directly opened to the outside air, a suction port 21 of the indoor air is installed at the base section near the floor face of the wall, and it is connected to the pipe end 7a of the intake pipe 7 of the sterilization duct 20 by a suction duct 22. When fans 10 and 11 stored in the sterilization duct 20 are operated, the indoor air is sucked into the suction port 21 and passes the sterilization zone 2 of the sterilization duct 20 via the suction duct 22. The sterilization zone 2 has a ultraviolet ozone-less lamp 4, the air containing bacteria is powerfully sterilized while passing there, and it is blown into the room through a blowout port 23 as the sterilized air. The indoor air is repeatedly circulated and sterilized through the sterilization duct 20.