To provide a water sealing device capable of efficiently discharging drain while maintaining airtightness inside an airtight chamber.

In the water sealing device 300, a first flow passage 101 can be blocked or communicated in accordance with a liquid level of drain in a first valve chamber 120, and the first flow passage 101 and a second valve chamber 150 can be blocked or communicated with each other in accordance with a pressure difference between pressure outside a cabin and water head pressure of drain. Thus, since the drain flow passage (the first flow passage 101, and the first flow passage 101 and the second valve chamber 150) is blocked or communicated in accordance with the necessity for discharging drain and the necessity for maintaining airtightness inside the cabin, the drain can be discharged efficiently. Even when the first valve chamber 120 has no drain, airtightness within the cabin can be maintained.