Abstract: An engine with an exhaust passage in which a catalyst purifying NOx and an NOx adsorbent adsorbing NOx in an exhaust gas are arranged successively from the upstream side. After engine startup until the catalyst is activated, the NOx in the exhaust gas is adsorbed at the NOx adsorbent. NOx adsorbed at the NOx adsorbent is removed by dissolution by supplying a solvent from an injector. After the catalyst is activated, the solvent containing the NOx removed by dissolution is sprayed from an injector and the NOx contained in the sprayed solvent is purified by the catalyst.