A crystalline magnesium oxide layer is placed facing the discharge space between a front glass substrate and a back glass substrate. The crystalline magnesium oxide layer contains crystal powder having particle-size distribution in which a crystal of a predetermined particle diameter or larger is included at a predetermined ratio or higher, of powder of a magnesium oxide crystal causing a cathode-luminescence emission having a peak within a wavelength range of 200 nm to 300 nm upon excitation by an electron beam.