PURPOSE: To dissolve disadvantage in the case of negative pressure acting upon the outer window glass of a vehicle.

CONSTITUTION: When a train enters a tunnel or passes by an opposed train, the outside pressure of the train is fluctuated in large degree, and according to the pressure fluctuation, a diaphragm 12 moves as shown by an imaginary line. That is, when the outside pressure becomes high, the diaphragm 12 is deformed in the direction of reducing the volume of a first pressure chamber S1, and when the outside pressure becomes low, the diaphragm 12 is deformed in the direction of enlarging the volume of the first pressure chamber S1. As a result, the outside pressure and the pressure of a space S3 become approximately equal.