PURPOSE: To lower the specific fuel consumption of an engine and to increase the engine output considerably, by providing a basic injection circuit for detecting the quantity of intake air and an injection timing controlling circuit including an injection timing determining means and a fuel supply means.

CONSTITUTION: A basic injection circuit 14 calculates the basic injection quantity of fuel from the output signals of a crank-angle sensor 17 and a water-temperature sensor 9. An injection timing controlling circuit 15 calculates the injection timing and duration of the basic injection quantity and controls operation of injectors 5. At the time of low-load operation of an engine, the injection starting timing is set substantially at the latter half of the suction stroke while the injection terminating timing is set at the end of the suction stroke. At the time of high-load operation of the engine, on the other hand, fuel is supplied throughout the suction stroke. With such an arrangement, it is enabled to lower the specific fuel consumption at the time of low-load operation of the engine by enabling combustion of lean mixture and to increase the engine output considerably at the time of high-load operation by raising the utilization factor of air.