A chabazite-type zeolite having copper and an alkali earth metal supported thereon. The alkali earth metal is preferably at least one metal selected from the group consisting of calcium, magnesium and barium. Moreover, the SiO2/Al2O3 molar ratio is preferably from 10 to 50, and the copper/aluminum atomic ratio is preferably from 0.15 to 0.25. This type of chabazite-type zeolite exhibits a higher nitrogen oxide purification rate after a hydrothermal durability treatment than those of conventional chabazite-type zeolite catalysts on which only copper is supported.