The invention relates to compound alkaline earth metal oxide containing magnesium oxide and other alkaline earth metal oxide. The invention provides material for film. The film contains magnesium oxide and other alkaline earth metal oxide and having low hygroscopicity, and having high secondary electron yield by adopting physical vapor phase growth methods such as an electron beam evaporation method or a sputtering method. The compound alkaline earth metal oxide includes magnesium oxide and other alkaline earth metal oxide at a mole ratio of Mg and other alkaline-earth metals which is 98:2 - 80:20. And the relative density is in a ranges of 95.0 -99.9 percents. The compound alkaline earth metal oxide further includes oxide containing at least one metallic element having one valency of 3, 4 or 5. The content of the oxide containing the metallic element is 1 mole relatively to the alkaline earth metal. The volume of the metallic elements is taken in a range of 0.0002 to 0.1 moles.