Fuel injection amount control device

A fuel injection amount control device configured to control a fuel injection amount of an injector in an internal combustion engine, wherein the internal combustion engine includes a blow-by gas ventilation system, which discharges blow-by gas leaking into a crankcase to an intake air, the fuel injection amount control device comprising:

• an air-fuel ratio feedback correction section, which corrects the fuel injection amount such that an air-fuel ratio approaches a target air-fuel ratio based on an air-fuel ratio detection result;
• a reflection rate setting section, which sets a reflection rate proportional to the amount of the blow-by gas discharged to the intake air;
• a dilution correction section, which corrects the fuel injection amount by using, as a correction value, a product obtained by multiplying the reflection rate by a dilution learning value;
• and
• a dilution learning section, which updates the dilution learning value such that a correction amount of the fuel injection amount obtained by the air-fuel ratio feedback correction section approaches.