An exhaust gas purifying apparatus adopted to an internal combustion engine provided with air-fuel ratio learning means for learning a primary air-fuel ratio given in the form of a mass ratio between air and fuel introduced into a combustion chamber, comprises an exhaust gas purifying catalyst provided in an exhaust gas passage of the engine and a catalyst activating means for supplying secondary air to an upstream of the exhaust gas purifying catalyst and increasing the quantity of fuel supplied to the engine to activate the exhaust gas purifying catalyst. The apparatus further comprises air-fuel ratio learning determining means for, when the internal combustion engine is started, determining whether or not learning of the primary air-fuel ratio by the air-fuel ratio learning means is completed; and activation control means for, when determined that the learning of the primary air-fuel ratio is not completed, prohibiting supply of the secondary air and increase of the quantity of fuel by the catalyst activation means.