To require no throttle position and negative pressure sensors, eliminate the need for providing a mounting space or structure for these sensors on a car body side and achieve easy mounting even on a small-sized vehicle.

In a fuel injection type internal combustion engine, an engine load is detected in accordance with the degree of rotational fluctuation of a crankshaft and a fuel injection amount is controlled in accordance with the detected engine load. The engine load detected from the degree of the rotational fluctuation is changed with an engine speed and so the engine load is desirably corrected in accordance with the engine speed if the engine speed has a wide range of change, in particular. Namely, the engine load is desirably found from the degree of the rotational fluctuation and the engine speed.