To provide a catalyst which has excellent durability and high oxygen reduction ability without being corroded in an acidic electrolyte or in a high electrical potential.

The catalyst is a metal carbon-nitrogen oxide containing one or more compounds of group 3 transition metals, and one or more oxides of group 4 transition metals or group 5 transition metals, which have 1-100 nm crystallite size. The one or more compounds of group 3 transition metals are one or more compounds of metals selected from the group consisting of scandium, yttrium, lanthanum, cerium, samarium, dysprosium and holmium. The one or more oxides of group 4 transition metals or group 5 transition metals are one or more oxides of metals selected from the group consisting of titanium, zirconium, tantalum and niobium.

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