An exhaust gas purifying device for an internal combustion engine, comprises: an exhaust purifying catalyst; a NOx purifying catalyst disposed downstream of the exhaust purifying catalyst; upstream and downstream A/F detecting sensors disposed on upstream and downstream sides of the exhaust purifying catalyst, respectively; means for supplying a reducing agent to the NOx purifying catalyst when conducting a reduction control of the NOx; means for calculating an amount of reduced NOx in the NOx purifying catalyst; means for terminating the reduction control when the amount of reduced NOx exceeds a prescribed reduction termination threshold value; means for detecting a degree of deterioration of the exhaust purifying catalyst based on an output from the upstream and downstream A/F detecting sensors; a threshold value correcting means for correcting the reduction termination threshold value according to the degree of deterioration of the exhaust purifying catalyst; and a correction prohibiting means for prohibiting the correction of the reduction termination threshold value when an amount of H2 and/or CH4 in the exhaust gas exceeds a prescribed correction prohibiting judgment value.