Exhaust purification device

(canceled)

An exhaust purifier wherein compressed air is injected into a catalyst reactor in which a NOx catalyst is arranged so as to remove dust adhering to the NOx catalyst,

• characterized in that
• when a pressure difference between exhaust gas upstream the NOx catalyst and exhaust gas downstream thereof is raised higher than a pressure difference between exhaust gas upstream the NOx catalyst and exhaust gas downstream thereof at an initial state at the same exhaust flow rate for not less than a permissible pressure difference raising amount, abnormal degradation of the NOx catalyst is judged to occur and notified to the outside, and
• existence of the abnormal degradation of the NOx catalyst is judged from a lowering rate of a denitration rate presumed based on a rising amount from the pressure difference between the exhaust gas upstream the NOx catalyst and the lowering rate of the denitration rate presumed from a NOx density of the exhaust gas before passing through the NOx catalyst and a NOx density of the exhaust gas after passing through the NOx catalyst detected by a NOx density detection means.