An abnormality diagnosis apparatus includes an exhaust gas purification apparatus arranged in an exhaust passage of an internal combustion engine and including a SCR catalyst; a supply apparatus supplying an additive such as ammonia to the exhaust gas purification apparatus; an EGR apparatus recirculating a part of exhaust gas from the exhaust passage at a downstream side of a position of supplying the additive to an intake passage; obtaining means for obtaining a NOx inflow amount into the exhaust gas purification apparatus; diagnosing means for calculating a physical quantity correlated to a NOx purification performance of the exhaust gas purification apparatus using the obtained NOx inflow amount, and diagnosing that an abnormality has occurred in the exhaust gas purification apparatus when the physical quantity is smaller than a threshold; and correcting means for, when the additive is recirculated together with a part of the exhaust gas, correcting the threshold to a smaller value than when otherwise.