To provide an abnormality determination device for an exhaust emission control system, capable of suppressing false determination.

This abnormality determination device is applied to the exhaust emission control system provided with an exhaust gas recirculation system performing exhaust gas recirculation for returning exhaust gas to a combustion chamber of an engine, a reducing agent supply device for supplying a reducing agent to exhaust gas, and a catalyst device for purifying exhaust gas in the downstream side of exhaust gas from the reducing agent supply device. The abnormality determination device is constituted so as to determine whether or not an abnormality occurs in each of the devices, in order from the devices arranged in the upstream side of exhaust gas, in concrete, in order of the exhaust gas recirculation system (S104), the reducing agent supply device (S108) and the catalyst device (S112). At this time, a result of the abnormality determination of the exhaust gas recirculation system is reflected on the abnormality determination of the reducing agent supply device and the catalyst device, and a result of the abnormality determination of the reducing agent supply device is reflected on the abnormality determination of the catalyst device.