An electronically-controlled fuel injection system includes electromagnetic fuel injection valves each of which is mounted in each cylinder of an internal combustion engine, and the injection of fuel during the starting period of the engine is also effected only by these fuel injection valves. During the starting period of the engine, the duration of the opening of the fuel injection valves is controlled at a constant value irrespective of the rotational speed of the engine until the rotational speed reaches a value corresponding to the initial combustion of fuel in the engine, after which the duration of the opening of the fuel injection valves is controlled in relation to the rotational speed of the engine. Further, during the time that the starter motor is in operation, the duration of the opening of the fuel injection valves which was basically determined in the previously mentioned manner is increased to a great extent in accordance with the temperature of the engine until the engine rotational speed reaches a value corresponding to the complete combustion of fuel in the engine.