PROBLEM TO BE SOLVED: To suppress discharge of unreacted sterilization substances to the minimum and to put an isolator into a state in which next work can be started as early as possible in performing sterilization processing between last work and the next work.SOLUTION: An isolator 100 is provided with: a work chamber 10 a gas supply part 40 a fan 46 a gas exhaust part 50 a sterilization substance reduction processing part 54 a concentration measurement part 56 a path 74 having a HEPA filter 20 a sterilization substance supply part 30 and a control unit 90. The control unit 90 first keeps concentration of the sterilization substance of the work chamber 10 fixed by supplying the sterilization substance to the work chamber 10, performs sterilization, starts exhaust by using the fan 46, and makes an exhaust speed when ending discharge faster an exhaust speed when the concentration of the sterilization substance reaches the highest. Thus, it is possible to suppress discharge of unreacted sterilization substance to the minimum and to shorten a time for sterilization processing by efficient exhaust.
