The interiors of casings 13, 14a, 14b and 14c of a base portion 11 and an operating arm 12 of a robot 3 placed in an isolator 1 communicate with each other for passage of a gas. A top end opening 25a of a vent tube 25 connected to a gas feed device 21 in a gas supply unit 4 provided outside the isolator extends through the casings and opens inside end casing 14a. A drawing device 23 in the air supply unit communicates with a base portion opening 13a formed in the base portion. At the time of sterilization of the isolator, the pressure inside the isolator is increased relative to the pressure inside the robot, and the gas supply unit is operated to cause a flow of a gas inside the robot from the casing 14a to the casing 13, thereby preventing any internal portion of the robot from being corroded by the sterilizing gas.