Abstract: Disclosed is a fuel injection quantity control system incorporated with a fuel injection pump with a solenoid-operated spill valve wherein a control signal is generated for cutting off a fuel supply to engine cylinders when a rotational phase angle of a drive shaft of the fuel injection pump is coincident with a desired spill phase angle determined in accordance with engine operating conditions. The desired spill phase angle, i.e., the opening timing of the spill valve is controlled in accordance with the rotational variations of the fuel injection pump. The desired spill phase angle is divided by unit angle corresponding to a detection period of rotational angle signals produced in accordance with the rotation of the pump drive shaft, obtaining a quotient and a remainder angle. The remainder angle is converted into a time on the basis of an engine speed.