PURPOSE: To permit the average air-fuel ratio of all cylinders to be set within the permissible error range by detecting the air excessive rate in the exhaust gas from a specific cylinder and controlling the amount of fuel injection of all fuel injection valves according to the results of detection.

CONSTITUTION: In a multicylinder-type internal combustion engine in which the amount of fuel which is supplied through injection process into each cylinder from fuel injection valves 121W124 is feedback-controlled according to the excessive rate of air in the exhaust gas which is detected by an O2 sensor 13, said O2 sensor 13 is installed in the vicinity of a connecting flange 10 acting as a connection of an internal combustion engine 1, to one branched pipe part 91 forming an exhaust manifold 8. In a controller 20, the standard fuel injection amount is calculated on the basis the signals from a revolution number sensor 21 and an air-flowmeter 3. Said injection amount is corrected according to the excessive rate of air in the exhaust gas which is detected by the O2 sensor 13, and fuel injection valves 121W124 are controlled by thus corrected fuel injection amount signal.