PURPOSE: To enable a specified amount of fuel to be sprayed into a combustion chamber from an injector at all times irrespective of any variation in atmospheric pressure and soon.

CONSTITUTION: In a fuel injection controller, a fuel pump 12 pumps out fuel in a fuel tank 11, discharging it toward a pressure regulator, and an injector 20 sprays fuel held at constant pressure into a combustion chamber A by the pressure regulator. A flow characteristic detecting means detects a flow characteristic of fuel, and on the basis of the detected flow characteristic, an injection quantity compensation means compensates the fuel injection quantity by the injector 20 so as to make it come to the specified value. Therefore, any possible reduction in the fuel injection quantity out of the injector with a drop in the atmospheric pressure, etc., is thus prevented, and since a specified amount of fuel is always sprayed into the combustion chamber, the proper operation of an engine will in no case be prevented by variations in the fuel injection quantity.