Exhaust purifying apparatus for internal combustion engine

The invention provides an exhaust purifying apparatus for internal combustion engine. The apparatus comprises a NOx purification catalyst, an oxidation catalyst, a NOx amount calculating part, and a control part. The NOx purification catalyst is arranged on the gas discharge route, and utilizes the urea water added in the discharged gas to purify NOx in discharged gas. The oxidation catalyst is arranged in the gas discharge route and is in a downstream position compared with the NOx purification catalyst. The NOx amount calculating part can calculate the NOx amount in discharged gas that goes through the oxidation catalyst. The control part can carry out abnormal situation diagnosis and treatment, when the NOx purification rate, which is calculated on the basis of calculated NOx amount, is lower than a rated value, which means that the NOx purification catalyst is abnormal; when the conditions of executing abnormal situation diagnosis and treatment are met, the abnormal situation diagnosis and treatment are executed, after the unburned fuel is separated from the NOx purification catalyst.