In a solid solution system of Al2O3 and CAO or SrO, it has been difficult to obtain a material having a high electrical conductivity (>10−4 S·cm−) at room temperature.A compound is provided in which electrons at a high concentration are introduced into a 12CaO.7Al2O3 compound, a 12SrO.7Al2O3 compound, or a mixed crystal compound containing 12CaO.7Al2O3 and 12SrO.7Al2O3. The compound formed by substituting all the free oxygen ions with electrons is regarded as an electride compound in which [Ca24Al28O64]4+(4e−) or [Sr24Al28O64]4+(4e−) serves as a cation and electrons serve as anions. When a single crystal or a hydrostatic pressure press molded material of a fine powder thereof is held at approximately 700° C. in an alkaline metal vapor or an alkaline earth metal vapor, melt of a hydrostatic pressure press molded material of a powder is held at approximately 1,600° C. in a carbon crucible, followed by slow cooling for solidification, or a thin film of the compound held at approximately 600° C. is implanted with rare gas ions, a great number of the free oxygen ions can be substituted with electrons.