PURPOSE: To improve detection precision of an engine rotational angle at a low speed territory where engine speed is low in a fuel injection pump of a diesel engine controlling fuel injection quantity by driving and controlling a spill valve.

CONSTITUTION: Two rotational angle sensors 35a, 35b are arranged on an engine speed detector 35 to compute fuel injection quantity in the state they are reciprocally offset by half a cycle of a unit pulse against a pulsar 7. Precision of fuel injection control is improved by computing fuel injection time by way of taking a detection pulse from the two rotational angle sensors 35a, 35b in a low speed territory where engine speed of an engine is low. Additionally, increase of capacity of a CPU is not required by computing it by a pulse from one of the rotational angle sensors in a high engine speed territory.