A three-way catalyst containing an oxygen occludable material has conventionally been known as one of catalysts that are interposed in the exhaust systems of vehicles driven by the power of gasoline. A three-way catalyst simultaneously promotes reduction of oxygen nitride (NOx), oxidization of hydrocarbon (HnCm), and oxidization of carbon monoxide (CO) in an atmosphere close to the stoichiometric air-fuel ratio. An oxygen occludable material is a promotor having characteristics that adsorbs oxygen under a lean atmosphere, and releases the oxygen occluded during lean running under a rich atmosphere. Examples of an oxygen occludable material are Ceria (CeO2), Ceria-Zirconia composite (CeO2—ZrO2), Almina-Ceria-Zirconia composite (Al2O3—CeO2—ZrO2), and composites of the above materials and second or third element components. Including the above oxygen occludable material in a catalyst easily maintain the oxygen concentration around the active site of the catalyst to the concentration near the stoichiometric air-fuel ratio. This ensures the air-fuel ratio to obtain preferable catalytic activity, so that the ability of the catalyst for purifying exhaust gas can be enhanced. The oxygen occluded on the oxygen occludable material is used in oxidization of hydrocarbon, carbon monoxide, and hydrogen (see Patent Literature 1).