An apparatus for controlling an air-fuel ratio in internal combustion engines has an RPM sensor, a combustion composition sensor, an intake air sensor and so on. Detection signals from these sensors are fetched by a microprocessor. A RAM is arranged in the microprocessor and is continuously supplied with power. The RAM has a first memory area which is divided into a plurality of areas for storing correction data corresponding to operating states of the engine. All the correction data stored in the first memory area are added together and the sum is divided by a given constant so as to obtain an updated correction amount. This updated correction amount is stored in a second memory area. The updated correction amount in the second memory area reflects the correction data stored in the first memory area. Given correction data stored in the first memory area is read out corresponding to a given intake air flow, thereby enabling feedback control.