A fuel injection control device

In a fuel system of an internal combustion engine, a fuel pressure sensor is disposed on a high pressure fuel pipe connecting common rail and a fuel injection valve. An electronic control unit (ECU) of the engine calculates the magnitude P of the fuel pressure fluctuation from the fuel pressure detected by the pressure sensor when a pilot fuel injection is executed. The ECU calculates the actual amount Qpl of the pilot fuel injection from the magnitude P and pressure Pc in the high pressure fuel pipe based on the relationship between Qpl and p, Pc determined beforehand by experiment. The ECU further corrects the fuel injection period of the fuel injection valve in such a manner that the difference dQpli between the actual amount Qpl and a target amount Qplt of pilot fuel injection becomes within an allowable range. Thus, the fuel injection amount of the fuel injection valve always agrees with the target fuel injection amount even if a fuel injection characteristics have changed after long period of operating the engine.