Disclosed are an exhaust gas cleaning apparatus of an internal combustion engine, which is provided with a three-way catalytic converter, and an air injection system responsive to the air-fuel ratio of the exhaust gas in the exhaust pipe for increasing or decreasing the amount of secondary air directed to the exhaust pipe so that the air-fuel ratio in the converter is maintained near the stoichiometric value. Means are provided for obtaining a high rate of increase in the introduction of secondary air when the acceleration pump is operated for introducing an amount of excess fuel into the engine during acceleration of the engine. Thus, the air fuel ratio occurring during this condition can be effectively controlled near the stoichiometric value.