The invention provides an exhaust purification device capable of suppressing the temporal decrease in NOx catalyst removal efficiency due to soot accumulation. The invention provides an exhaust purification device using an air injection nozzle to inject pressurized air into a casing of a catalyst reactor containing an NOx catalyst as a catalyst and removing soot adhering to the NOx catalyst, wherein it is determined and externally notified that there is abnormal deterioration in the NOx catalyst when the pressure difference ΔP in exhaust between the upstream and downstream sides of the NOx catalyst has increased by at least a first reference pressure difference increase ΔPt1, which is the allowable amount of pressure difference increase, above the pressure difference ΔPi in exhaust between the upstream and downstream sides of the catalyst in the initial state at the same exhaust flow rate Ve.