Abstract: A multiple cylinder engine including a first group of cylinders having a first intake passage which is provided with a air-fuel mixture of a predetermined ratio in accordance with the signal from an exhaust gas sensor provided in the exhaust passage from the first group of cylinders. The engine further includes a second group of cylinders having a second intake passage which is provided with a mixture having an air-fuel ratio which is of a predetermined relationship with respect to the air-fuel ratio of the mixture provided to the first group of cylinders, the predetermined relationship being determined in accordance the engine operating condition. Check valves are provided in the intake passages to prevent the mixture in the first intake passage from being mixed with that in the second intake passage so that accurate control can be ensured.