To level air-fuel ratio for respective cylinders by absorbing dispersion of air-fuel ratios among engine cylinders and mechanical detection dispersion of a crank angle.

First and second AF sensors 29A, 29B are arranged in a gathering exhaust passage of exhaust manifolds 20A, 20B communicating and combining respectively with the cylinder #1 on a right bank RH and the cylinder #2 on a left bank LH and the cylinder #3 on the right bank RH and the cylinder #4 on the left bank LH which are not next to each other in combustion order. The air-fuel ratios of the respective cylinders are detected in a sample range of the crank angle set according to exhaust stroke of the respective cylinders and an air-fuel ratio feedback control is performed on the basis of deviation between the detected air-fuel ratio and the target air-fuel ratio of each cylinder. Thereby, the air-fuel ratios of the respective cylinders are accurately detected with canceling dispersion of air-fuel ratios among the cylinders and mechanical detection dispersion of the crank angle and combustion state of the respective cylinders are leveled.