PURPOSE: To effectively adsorb HC by an adsorber so as to prevent discharge of HC in the atmosphere, and suppress a discharge quantity of NOx when HC is separated from the adsorber.

CONSTITUTION: A bypass passage C is provided upstream from a catalyst device B, and an adsorber D is interposed in the bypass passage C. An exhaust induction period to the adsorber D is set based on a temperature of an engine, and then a valve device E is operated to have HC adsorbed by the adsorber D (F, G, H). Separation of HC from the adsorber D is performed when catalyst of the catalyst device B is activated and an operational condition of the engine is in its deceleration stage or the idle operation stage (I, J, K).