AIR/FUEL RATIO CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

A catalyst (52) having an oxidization capability is provided in an exhaust passage. After a rich control for controlling the air/fuel ratio of a mixture formed in a combustion chamber (25) to be an air/fuel ratio richer than the stoichiometric air/fuel ratio, a lean control is carried out so that the air/fuel ratio of the mixture formed in the combustion chamber is controlled to be an air/fuel ratio leaner by a predetermined degree than the stoichiometric air/fuel ratio, or the air/fuel ratio of the mixture formed in the combustion chamber is controlled to temporarily be the air/fuel ratio leaner by the predetermined degree than the stoichiometric air/fuel ratio. If the lean control is carried out after the rich control is finished, there is provided temporary lean control so that a degree of how much the air/fuel ratio of the mixture is leaner than the stoichiometric air/fuel ratio when the air/fuel ratio of the mixture formed in the combustion chamber is controlled to be the air/fuel ratio leaner than the stoichiometric air/fuel ratio in the lean control is lower than the predetermined degree according to the temperature of the catalyst.