With a V type engine, the exhaust air-fuel ratio is detected for each bank, and is also detected downstream of a catalytic converter which takes the combined exhaust flow from each bank. An air-fuel ratio feedback correction coefficient .alpha. is proportional-plus-integral controlled separately for each of the banks based on the air-fuel ratio detected for each of the banks, while a correction value PHOS for a proportional portion is set commonly for each of the banks, based on the air-fuel ratio detected downstream of the catalytic converter. Here the correction value PHOS is converted to separate correction values PHOSR, PHOSL for each of the banks corresponding to a change rate of the air-fuel ratio feedback correction coefficient .alpha. to an initial value, and the proportional operating amount of the proportional-plus-integral control which is carried out separately for each bank, is corrected based on the converted correction values PHOSR, PHOSL.With such construction, the proportional operating amount can be suitably corrected corresponding the difference in the base air-fuel ratios occurring between the banks, so that the air-fuel ratio of each bank can be controlled to a high accuracy.