A deterioration diagnosis apparatus applied to an exhaust gas purification apparatus provided with a first exhaust gas purification apparatus that is provided in an exhaust passage of an internal combustion engine capable of performing a lean burn operation, and includes a catalyst that is configured to promote a water-gas shift reaction when an air-fuel ratio of exhaust gas is a rich air-fuel ratio that is lower than a stoichiometric air-fuel ratio; and a second exhaust gas purification apparatus that is disposed in the exhaust passage downstream of the first exhaust gas purification apparatus, and includes a selective catalytic reduction catalyst that is configured to occlude oxygen contained in the exhaust gas when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio that is higher than the stoichiometric air-fuel ratio, and configured to release the occluded oxygen when the air-fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air-fuel ratio, characterized in that the deterioration diagnosis apparatus further comprises: a first sensor configured to measure a physical quantity that correlates with an oxygen concentration of exhaust gas flowing into the second exhaust gas purification apparatus; a second sensor configured to measure a physical quantity that correlates with an oxygen concentration of exhaust gas flowing out of the second exhaust gas purification apparatus; and a diagnosing means configured to diagnose deterioration of the second exhaust gas purification apparatus, and control means configured to execute induction processing, which is processing for inducing the water-gas shift reaction in the first exhaust gas purification apparatus, by modifying an air-fuel ratio of exhaust gas flowing into the first exhaust gas purification apparatus to a rich air-fuel ratio that is lower than the stoichiometric air-fuel ratio when the operating condition of the internal combustion engine is in the lean operation region, wherein the diagnosing means is configured to diagnose deterioration of the second exhaust gas purification apparatus using, as a parameter, a difference that appears between a measurement value of the first sensor and a measurement value of the second sensor when the induction processing is executed. a first sensor configured to measure a physical quantity that correlates with an oxygen concentration of exhaust gas flowing into the second exhaust gas purification apparatus; a second sensor configured to measure a physical quantity that correlates with an oxygen concentration of exhaust gas flowing out of the second exhaust gas purification apparatus; and a diagnosing means configured to diagnose deterioration of the second exhaust gas purification apparatus, and control means configured to execute induction processing, which is processing for inducing the water-gas shift reaction in the first exhaust gas purification apparatus, by modifying an air-fuel ratio of exhaust gas flowing into the first exhaust gas purification apparatus to a rich air-fuel ratio that is lower than the stoichiometric air-fuel ratio when the operating condition of the internal combustion engine is in the lean operation region, wherein the diagnosing means is configured to diagnose deterioration of the second exhaust gas purification apparatus using, as a parameter, a difference that appears between a measurement value of the first sensor and a measurement value of the second sensor when the induction processing is executed.