Disclosed is an internal combustion engine comprising a catalytic converter containing a three way catalyzer therein. A secondary air feed control device, an air-fuel ratio detector and the catalytic converter are arranged in this order in the exhaust passage of the engine. An exhaust gas mixing device is disposed in the exhaust passage between the air-fuel ratio detector and the catalytic converter so as to make a total air-fuel ratio in the inlet of the catalytic converter equal to the stoichiometric air-fuel ratio at all times.