To automatically regulate a fuel injection rate to a desired demand injection rate correctly and easily by arranging an injection rate regulating member for regulating the injection rate of a fuel injection pump, and carrying out control on the basis of the deviation between a detected fuel flow rate and a demand injection rate.

An injection rate regulating device 32 consists of a driving part 33 such as a pulse motor for driving the full load adjust screw of a fuel injection pump 1, an instant flow rate meter 34, a control circuit 35 and the like. When the command value of a demand injection rate outputted from a computer 40 is transmitted to a signal conditioner 41 and it is converted into an analog signal and then it is added on a control circuit 35, a deviation between the flow rate value of a real injection rate from the instant flow rate meter 34 and the command value of the demand injection rate is found out in the control circuit 35, and a signal corresponding to the deviation is outputted so as to control the pulse motor 33. The full load adjacent screw of the fuel injection pump 1 is rotated so as to regulate the injection rate.