PURPOSE: To always obtain the information of engine speed with a high degree of accuracy, by calculating the averaged speed of an engine in association with a pulse representing the top dead center timing, and then by discriminating abnormalities in the variation coefficient of fluctuation rate of engine speed in accordance with the above- mentioned averaged speed so that normal fluctuation rates alone are issued.

CONSTITUTION: A computing and processing device 4 computes the rotational speed of an engine in accordance with a timing pulse P which is delivered from a timing pulse generator 5 and which represents the top dead center timing of the engine, and then, computes a control signal in accordance with rotational speed data, accelerator data D1 and water temperature data D2. Therefore, a servo device 6 is controlled in accordance with the control signal to position the fuel adjusting member of a fuel injection pump 3. In this stage, the computing and processing device 4 further computes an averaged engine speed at every time when the pulse P is delivered, and as well computes the speed fluctuation rates of the engine at every time when (m) number of pulses P are generated. Then, abnormalities in the variation coefficient of fluctuation rates is discriminated so that normal fluctuation rates alone are issued as speed variation data.