An isolator (100) includes a work chamber (10), a gas supply unit (1040), a gas discharge unit (1050), a connection channel that has a particulate trap filter and connects the gas supply unit (1040) with the work chamber (1010) and a sterilizing substance supply unit (1030). A discharge means is configured to control the discharge amount of the gas that is discharged from the gas discharge unit (1050), while a reduction process unit is configured to reduce the concentration of the sterilizing substance that is contained in the gas discharged from the gas discharge unit (1050). A controller (1090) is configured to start discharge by using the discharge means after sterilizing the inside of the work chamber (1010) by supplying sterilizing substance into the work chamber (1010) to maintain the concentration of the sterilizing substance in the work chamber (1010) , and to make the discharge amount at the end of the discharge larger than that occurring when the concentration of the sterilizing substance reaches the maximum.
