A protective film (6) having a high secondary-emission coefficient is formed on a dielectric layer (5) so as to lower the discharge voltage of a plasma display panel. When the protective film (6) is exposed to the air, it will transform or become cloudy, or the secondary-emission coefficient will lower. To prevent this problem, an inert film (60) is formed on the surface of the protective film (6). As the inert film (60), a film of a metal oxide such as SiO2 and a film of a metal such as Tb are simultaneously formed. Thus, an inert film (60) excellent in barrier property against oxygen and water in the air and enabling easy sputtering from near the discharge electrode at the aging step can be obtained. With this, a plasma display panel exhibiting a low discharge voltage can be realized.