EXHAUST GAS PURIFIER FOR INTERNAL COMBUSTION ENGINES

An exhaust passage (20) of an internal-combustion engine (1) is provided with exhaust emission control means (40) capable of reducing harmful substances in exhaust gas under a given exhaust pressure condition and an exhaust sensor (22) for detecting the concentration of a specific exhaust component (H2, O2) in the exhaust gas, and performance lowering identifying means identifies lowering of the performance of the exhaust emission control means (40) by detecting a failure to fulfill the given exhaust pressure condition in accordance with the output of the exhaust sensor.