An object is to prevent a wrong diagnosis from being made in an abnormality diagnosis apparatus for an exhaust gas purification system including a filter and a PM sensor. After sensor regeneration is performed, the application of voltage to the PM sensor is started, and thereafter abnormality diagnosis of the PM sensor is performed based on whether or not a signal is output from the PM sensor. Abnormality diagnosis of the filter is performed based on whether or not the output value of the PM sensor reaches a predetermined abnormality criterion value. If the output value of the PM sensor reaches the predetermined abnormality criterion value before a predetermined diagnosis completion time after the abnormality diagnosis of the PM sensor, the filter is diagnosed as abnormal, and the application of voltage to the PM sensor is stopped at that time.