To efficiently purify NOx by purging an evaporated fuel mixture from an intake passage when NOx adsorbed by the NOx storing catalyst exceeds a specified reference value and shifting from stratified combustion to uniform combustion and supplying a stoichiometric or rich mixture to release NOx in an NOx storing catalyst.

The NOx storing quantity in a catalyst is estimated by an NOx storing quantity estimating means according to lean-burn operation duration and an operating state, and whether or not the NOx storing quantity exceeds the set reference value is judged by a combustion form determining means 54. In the case of exceeding the reference value, a combustion form is switched to uniform combustion, and purge gas concentration in evaporated fuel computed by a purge gas concentration computing means 52 is read by a canister purge time computing means 58 and compared with the set reference value. In the case of being the reference value or less or more, time to be canister purge execution time is respectively computed by the canister purge time computing means 58, and a purge valve 18 is controlled by a purge valve control means 56.