An abnormality diagnosis apparatus of an exhaust gas purification apparatus, comprising: an exhaust gas purification apparatus which is arranged in an exhaust passage of an internal combustion engine and which includes a selective catalytic reduction catalyst; a supply apparatus which supplies an additive that is ammonia or an ammonia precursor to the exhaust gas purification apparatus; an EGR apparatus which recirculates a part of exhaust gas from the exhaust passage at a downstream side of a position of supplying the additive by the supply apparatus to an intake passage; and a controller comprising: obtaining means adapted to obtain a NO x inflow amount that is an amount of NO x that flows into the exhaust gas purification apparatus; diagnosing means adapted to diagnose a physical quantity correlated to a NO x purification performance of the exhaust gas purification apparatus in use of the NO x inflow amount obtained by the obtaining means as a parameter, and to diagnose that an abnormality has occurred in the exhaust gas purification apparatus when a calculation result thereof is smaller than a threshold; and correcting means adapted to, when the additive is recirculated together with a part of the exhaust gas by the EGR apparatus, correct the threshold to a smaller value than when the additive is not recirculated together with a part of the exhaust gas by the EGR apparatus. an exhaust gas purification apparatus which is arranged in an exhaust passage of an internal combustion engine and which includes a selective catalytic reduction catalyst; a supply apparatus which supplies an additive that is ammonia or an ammonia precursor to the exhaust gas purification apparatus; an EGR apparatus which recirculates a part of exhaust gas from the exhaust passage at a downstream side of a position of supplying the additive by the supply apparatus to an intake passage; and a controller comprising: obtaining means adapted to obtain a NO x inflow amount that is an amount of NO x that flows into the exhaust gas purification apparatus; diagnosing means adapted to diagnose a physical quantity correlated to a NO x purification performance of the exhaust gas purification apparatus in use of the NO x inflow amount obtained by the obtaining means as a parameter, and to diagnose that an abnormality has occurred in the exhaust gas purification apparatus when a calculation result thereof is smaller than a threshold; and correcting means adapted to, when the additive is recirculated together with a part of the exhaust gas by the EGR apparatus, correct the threshold to a smaller value than when the additive is not recirculated together with a part of the exhaust gas by the EGR apparatus. obtaining means adapted to obtain a NO x inflow amount that is an amount of NO x that flows into the exhaust gas purification apparatus; diagnosing means adapted to diagnose a physical quantity correlated to a NO x purification performance of the exhaust gas purification apparatus in use of the NO x inflow amount obtained by the obtaining means as a parameter, and to diagnose that an abnormality has occurred in the exhaust gas purification apparatus when a calculation result thereof is smaller than a threshold; and correcting means adapted to, when the additive is recirculated together with a part of the exhaust gas by the EGR apparatus, correct the threshold to a smaller value than when the additive is not recirculated together with a part of the exhaust gas by the EGR apparatus.