An exhaust gas purification apparatus for an internal combustion engine, comprising: a filter which is provided in an exhaust gas passage of the internal combustion engine and which traps particulate matter contained in an exhaust gas, the filter including a selective catalytic reduction NOx catalyst carried thereon for reducing NOx contained in the exhaust gas by using ammonia as a reducing agent; an ammonia supply device configured to supply ammonia or an ammonia precursor to the filter; and a post-catalyst which is provided in the exhaust gas passage on a downstream side from the filter, characterized by the post-catalyst being constructed to include: an adsorption reduction part (81c; 8d) which has a function to adsorb ammonia and a function to reduce NOx by using ammonia as the reducing agent; a first oxidation part (81b; 8c) which is positioned on a downstream side from the adsorption reduction part (81c; 8d) along with a flow of the exhaust gas and which has a function to oxidize ammonia; and a second oxidation part (82; 8b) which is positioned on a downstream side from the adsorption reduction part (81c; 8d) and the first oxidation part (81b; 8c) along with the flow of the exhaust gas, which has an oxidation ability higher than that of the first oxidation part (81b; 8c), and which has a function to oxidize HC and CO. a filter which is provided in an exhaust gas passage of the internal combustion engine and which traps particulate matter contained in an exhaust gas, the filter including a selective catalytic reduction NOx catalyst carried thereon for reducing NOx contained in the exhaust gas by using ammonia as a reducing agent; an ammonia supply device configured to supply ammonia or an ammonia precursor to the filter; and a post-catalyst which is provided in the exhaust gas passage on a downstream side from the filter, characterized by the post-catalyst being constructed to include: an adsorption reduction part (81c; 8d) which has a function to adsorb ammonia and a function to reduce NOx by using ammonia as the reducing agent; a first oxidation part (81b; 8c) which is positioned on a downstream side from the adsorption reduction part (81c; 8d) along with a flow of the exhaust gas and which has a function to oxidize ammonia; and a second oxidation part (82; 8b) which is positioned on a downstream side from the adsorption reduction part (81c; 8d) and the first oxidation part (81b; 8c) along with the flow of the exhaust gas, which has an oxidation ability higher than that of the first oxidation part (81b; 8c), and which has a function to oxidize HC and CO. an adsorption reduction part (81c; 8d) which has a function to adsorb ammonia and a function to reduce NOx by using ammonia as the reducing agent; a first oxidation part (81b; 8c) which is positioned on a downstream side from the adsorption reduction part (81c; 8d) along with a flow of the exhaust gas and which has a function to oxidize ammonia; and a second oxidation part (82; 8b) which is positioned on a downstream side from the adsorption reduction part (81c; 8d) and the first oxidation part (81b; 8c) along with the flow of the exhaust gas, which has an oxidation ability higher than that of the first oxidation part (81b; 8c), and which has a function to oxidize HC and CO.