A clean air supply apparatus is provided which has an ability of sterilizing effectively and uniformly also a secondary side surface of a filter. The apparatus has a pre-filter 23 for roughly filtering air sequentially introduced from an air inlet port 18 for introducing air to an air supply port 22 for sending clean air to a work environment, a blower 24 for sucking air to the introduced, a heater 25 for adjusting a temperature of introduced air, a chemical agent gas supply apparatus 27, a chemical agent gas eject apparatus 26 for supplying chemical agent gas into the air path, high performance filters or ultrahigh performance filters 41 and 42 for filtering air to be delivered from an air supply port 22 to generate clean air.
