Fuel injection dose control device for engine

The present invention provides a fuel injection dose control device for an engine. The fuel injection dose control device uses the alpha-N mode to presume the air inflow Ga leaded into a combustion chamber more precisely and can control the fuel injection dose suitably according to the presumed air inflow. An electronic control device ECU (20) presumes the air inflow Ga according to the throttle percentage TA and the engine speed NE; and an injector (4) is controlled according to the fuel injection dose TAU calculated through the Ga. The ECU (20) performs the following operation during the operation of the engine: obtaining the current ISC flow corresponding to the current ISC control flow according to the ISC flow performance data; obtaining the first air inflow GaA corresponding to the TA and NE when the ISC flow becomes a minimum by referring to the first air inflow; obtaining the second air inflow GaB corresponding to the TA and NE when the ISC flow becomes a maximum by referring to the second air inflow; and according to the current ISC flow and the relationship between the maximum and the minimum of the ISC flow, performing interpolation between the GaA and the GaB, thus presuming the current Ga.