AIR-FUEL RATIO CONTROL APPARATUS FOR INTERNAL COMBUSTION ENGINE AND AIR-FUEL RATIO CONTROL METHOD THEREFOR

An air-fuel ratio control apparatus includes an air-fuel ratio control unit controlling an air-fuel ratio of exhaust gas flowing into an exhaust gas control catalyst of the internal combustion engine includes an air-fuel ratio control unit controlling the air-fuel ratio of the exhaust gas flowing into the exhaust gas control catalyst. The air-fuel ratio control unit alternately repeats a rich process for controlling the air-fuel ratio that is richer than a stoichiometric air-fuel ratio and a lean process for controlling the air-fuel ratio hat is leaner than the stoichiometric air-fuel ratio. The air-fuel ratio control unit, during the rich process, executes a lean pulse process for controlling, over a period shorter than a period of one execution of the lean process, the air-fuel ratio of the exhaust gas to reach a lean air-fuel ratio having a higher lean level than the air-fuel ratio during the lean process.