A first NOx adsorption material 20 exhibiting a peak temperature being 200° C. or less at which an elimination amount of adsorbed NOx becomes the maximum is put in place on an exhaust-gas upstream side, and a second NOx adsorption material 21 exhibiting a peak temperature surpassing 200° C. at which an elimination amount of adsorbed NOx becomes the maximum is put in place on an exhaust-gas downstream side of the first NOx adsorption material 20. In low-temperature region, NOx are adsorbed on the first NOx adsorption material 20; and, in high-temperature region, NOx having been eliminated from the first NOx adsorption material 21 are adsorbed on the second NOx adsorption material 21 again. Therefore, it is possible to adsorb NOx form low-temperature region and up to high-temperature region efficiently, and thereby an amount of NOx being discharged from an NOx reduction catalyst to be put in place on a downstream-side thereof is reduced.