PROBLEM TO BE SOLVED: To provide a technique for ventilating the inside of an endoscope and the outside of a simple sterilization bag while the endoscope is housed in the sterilization bag.SOLUTION: A ventilation adapter 170 is inserted into an adapter opening part 152 of the sterilization bag 150, and one end of the ventilation adapter 170 is mounted on an endoscope connector 62 of the endoscope 10 housed in the sterilization bag 150. Thus, the outer side of the sterilization bag 150 where the other end of the ventilation adapter 170 is arranged and the inside of the endoscope 10 are communicated through the ventilation adapter 170. Particularly, by connecting a connection connector 74 of a ventilation device such as an airtightness tester to the other end of the ventilation adapter 170, the inside of the endoscope 10 and the ventilation device are ventilated through the ventilation adapter 170 and the connection connector 74.
