A cold cathode fluorescent tube where an electron emitting electrode is sealed in shows much deterioration in the luminance with time, thereby being not adequate for a long time use. The electrode emitting electrode is formed in such a shape that an electric field is not locally concentrated. By mixing a material of high heat conductivity, such as tungsten, as the material for the electron emitting electrode or using helium of high heat conductivity as the sealing gas, a long life of the cold cathode fluorescent tube is achieved.