An exhaust gas purification apparatus for an internal combustion engine comprising: an addition valve that is arranged in an exhaust passage of the internal combustion engine, and configured to add a precursor of ammonia or ammonia into said exhaust passage; a sensor that is arranged in said exhaust passage at a location upstream of said addition valve, and configured to detect NOx and ammonia in the exhaust gas; a channel cross section reducing part that is arranged in said exhaust passage at a location downstream of said addition valve and has a flow passage for exhaust gas which is smaller in cross section than the exhaust passage at the upstream side of said addition valve; and a control device configured to calculate an amount of the precursor of ammonia or an amount of ammonia to be added from said addition valve based on the detection value of said sensor, or a rate of NOx reduction based on the detection value of said sensor; characterized in that: in cases where the flow rate of the exhaust gas flowing through said exhaust passage is equal to or more than a predetermined flow rate, said control device is configured to perform limitation of the calculation of the amount of the precursor of ammonia or the amount of ammonia to be added from said addition valve, or of the calculation of the rate of NOx reduction by calculating the amount of the precursor of ammonia or the amount of ammonia to be added from said addition valve, or by calculating the rate of NOx reduction not using the detection value of said sensor, using the detection value of said sensor after being corrected or using the detection value of said sensors and correcting the calculated amount of the precursor of ammonia or the amount of ammonia to be added from said addition valve, or by correcting the calculated rate of NOx reduction. an addition valve that is arranged in an exhaust passage of the internal combustion engine, and configured to add a precursor of ammonia or ammonia into said exhaust passage; a sensor that is arranged in said exhaust passage at a location upstream of said addition valve, and configured to detect NOx and ammonia in the exhaust gas; a channel cross section reducing part that is arranged in said exhaust passage at a location downstream of said addition valve and has a flow passage for exhaust gas which is smaller in cross section than the exhaust passage at the upstream side of said addition valve; and a control device configured to calculate an amount of the precursor of ammonia or an amount of ammonia to be added from said addition valve based on the detection value of said sensor, or a rate of NOx reduction based on the detection value of said sensor; characterized in that: in cases where the flow rate of the exhaust gas flowing through said exhaust passage is equal to or more than a predetermined flow rate, said control device is configured to perform limitation of the calculation of the amount of the precursor of ammonia or the amount of ammonia to be added from said addition valve, or of the calculation of the rate of NOx reduction by calculating the amount of the precursor of ammonia or the amount of ammonia to be added from said addition valve, or by calculating the rate of NOx reduction not using the detection value of said sensor, using the detection value of said sensor after being corrected or using the detection value of said sensors and correcting the calculated amount of the precursor of ammonia or the amount of ammonia to be added from said addition valve, or by correcting the calculated rate of NOx reduction.