In order to be capable of high-precision gas measurement and evaluating influences of a gas on an electron source, and to predict a life of an image display device with high precision for a short period of time, there is provided a sealed container which is capable of maintaining an inside thereof to a lower pressure than an atmospheric pressure, and is used for an image display device including in the inside: a phosphor; an electron-emitting device for causing the phosphor to emit light; and a getter, the sealed container including an exhaust pipe having a breakable vacuum isolating member on at least one side of the image display device. Accordingly, after the exhaust pipe is connected to a gas measuring apparatus, by vacuum-exhausting the gas measuring apparatus and breaking the breakable vacuum isolating member, it is possible to perform a gas measurement on the image display device by using a measuring chamber having an orifice having a known conductance and installed in part of an exhaust channel of the gas measuring apparatus for vacuum-exhausting the image display device.