An exhaust gas purification apparatus for an internal combustion engine includes an addition valve to add a precursor of ammonia or ammonia into an exhaust passage of the internal combustion engine, a sensor to detect NOx and ammonia at the upstream side of the addition valve, a channel cross section reducing part arranged at the downstream side of the addition valve, and a control device to limit the calculation of an amount of the precursor of ammonia or an amount of ammonia to be added from the addition valve based on a detection value of the sensor, or the calculation of a rate of NOx reduction based on the detection value of the sensor, in cases where a flow rate of exhaust gas flowing through the exhaust passage is equal to or more than a predetermined flow rate.