[Problem] Many oxide-ion conductors exhibit high functionality at high temperatures due to the large weight and charge of oxide ions, and it has been difficult to achieve the functionality at low temperatures.[Solution] A perovskite oxide having hydride ion conductivity, at least 1 at % of the oxide ions (O2−) contained in a titanium-containing perovskite oxide being substituted with hydride ions (H−). This oxide, in which negatively charged hydride ions (H−) are used for the ionic conduction, has both hydride ion conductivity and electron conductivity. As a starting material, the titanium-containing perovskite oxide is kept together with a powder of an alkali metal or alkaline-earth metal hydride selected from LiH, CaH2, SrH2, and BaH2 in a temperature range of 300° C. or higher and lower than the melting point of the hydride in a vacuum or an inert gas atmosphere to substitute some of the oxide ions in the oxide with the hydride ions, resulting in the introduction of the hydride ions into oxygen sites.