PURPOSE: To keep an air-fuel ratio at a constant value and to prevent the fluctuation of combustion due to the fluctuation of an air-fuel ratio and in turn to prevent the fluctuation of rotation of an engine by a method wherein control is performed in such a manner that at a low speed low load operation area, a throttle opening and a fuel injection amount are adjusted to a constant throttle opening and a constant fuel amount, which are set based on a target air-fuel ratio.

CONSTITUTION: In an ECU 30 to control the cylinder injection type two-cycle V-type six-cylinder engine 2 of an outboard engine, when a throttle operation amount by a steersman is within a given range and the number of revolutions of an engine is approximately 2500rpm or less, it is decided by an operation area detecting means 30a that an engine operation area is in a low speed low load operation area. At the operation area, a throttle opening is controlled to a constant value of approximate 18° through a throttle drive mechanism 28 by a throttle control means 30b in spite of a throttle operation amount. A fuel injection amount is determined according to an intake air amount by an injection amount control means 30c when a throttle opening is kept at a constant value and an injection time by a fuel injection valve 13 is controlled.