To suitably control the supply quantity of a reducing agent according to the emission quantity of specific components by a simple and low cost structure, in an exhaust gas treatment device provided with a selective reduction type catalyst.
This device includes a reducer supply means 4 supplying reducer to exhaust gas discharged from an internal combustion engine 1, a selective reduction type catalyst 5 selectively reducing specific component in exhaust gas via the reducer, a specific component detection means 8 disposed at an exhaust gas downstream side of the selective reducer type catalyst 5 and detecting specific component in exhaust gas, and a feedback control means 10 correcting supply quantity of the reducer supplied from the reducer supply means 4 by increasing and decreasing the same to keep the specific component at a prescribed level via feedback correction coefficient to the base supply quantity, The feedback control means 10 updates and stores a long term feedback correction coefficient based on the feedback correction coefficient in a relatively long term, and sets the feedback correction coefficient based on the long term feedback correction coefficient.
NINOMIYA HIROYUKI
SHIMIZU TAKAHARU
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