An intake port (4) is connected to a combustion chamber (6) of an internal combustion engine (1) via an intake valve (15), and a volatile liquid fuel is injected from a fuel injector (21) provided in the intake port (4). The controller (31) calculates a suspension ratio in the combustion chamber (5) of the injected fuel according to the particle diameter of the injected fuel (52-56), calculates an amount of fuel burnt in the combustion chamber (6) based on the suspension ratio (57), calculates a target fuel injection amount based on the burnt fuel amount (75, 76), and controls a fuel injection amount of the fuel injector (21) based on the target fuel injection amount (76). Precise fuel injection control can be performed without performing adaptation experiments, based on particle diameter data for different fuel injectors by taking the particle diameter as a parameter.