An exhaust gas control apparatus for an internal combustion engine, the internal combustion engine including an exhaust passage (19,21), the exhaust passage (19,21) including a three-way catalyst and an NO x adsorption catalyst, the NOx adsorption catalyst configured to adsorb NO x in exhaust gas when an air-fuel ratio of the exhaust gas introduced to the NOx adsorption catalyst is in a lean range, and the NOx adsorption catalyst configured to discharge the adsorbed NO x when the air-fuel ratio of the exhaust gas introduced to the NOx adsorption catalyst is changed to a rich range, the exhaust gas control apparatus comprising: an electronic control unit configured to control a combustion in a combustion chamber of the internal combustion engine at a first base air-fuel ratio when the internal combustion engine is operated in a predetermined low-load engine operation area, the first base air-fuel ratio being a lean air-fuel ratio; the electronic control unit being also configured to change the combustion in the combustion chamber to the rich range air-fuel ratio with a first periodicity when the internal combustion engine is operated in the predetermined low-load engine operation area and the NO x adsorption catalyst discharges the adsorbed NOx; the electronic control unit being also configured to control the combustion in the combustion chamber to a theoretical air-fuel ratio in a feedback manner when the internal combustion engine is operated in a predetermined high-load engine operation area; and characterized in that the electronic control unit is configured to control the combustion in the combustion chamber at a second base air-fuel ratio when the internal combustion engine is operated in a predetermined middle-load engine operation area, the second base air-fuel ratio being lower than the first base air-fuel ratio, the predetermined middle-load engine operation area being set between the predetermined low-load engine operation area and the predetermined high-load engine operation area; and the electronic control unit is configured to change the combustion in the combustion chamber to the rich range air-fuel ratio with a second periodicity when the internal combustion engine is operated in the predetermined middle-load engine operation area and the NO x adsorption catalyst discharges the adsorbed NOx, the second periodicity being shorter than the first periodicity. an electronic control unit configured to control a combustion in a combustion chamber of the internal combustion engine at a first base air-fuel ratio when the internal combustion engine is operated in a predetermined low-load engine operation area, the first base air-fuel ratio being a lean air-fuel ratio; the electronic control unit being also configured to change the combustion in the combustion chamber to the rich range air-fuel ratio with a first periodicity when the internal combustion engine is operated in the predetermined low-load engine operation area and the NO x adsorption catalyst discharges the adsorbed NOx; the electronic control unit being also configured to control the combustion in the combustion chamber to a theoretical air-fuel ratio in a feedback manner when the internal combustion engine is operated in a predetermined high-load engine operation area; and characterized in that the electronic control unit is configured to control the combustion in the combustion chamber at a second base air-fuel ratio when the internal combustion engine is operated in a predetermined middle-load engine operation area, the second base air-fuel ratio being lower than the first base air-fuel ratio, the predetermined middle-load engine operation area being set between the predetermined low-load engine operation area and the predetermined high-load engine operation area; and the electronic control unit is configured to change the combustion in the combustion chamber to the rich range air-fuel ratio with a second periodicity when the internal combustion engine is operated in the predetermined middle-load engine operation area and the NO x adsorption catalyst discharges the adsorbed NOx, the second periodicity being shorter than the first periodicity.