In a fuel injection control apparatus of an internal combustion engine for controlling a fuel supply quantities by making use of a fuel behavior model obtained by modeling the dynamic behavior of fuel flowing from injector into combustion chamber of cylinder of engine, the fuel behavior model is configured to estimate the dynamic fuel behavior such as attachment onto and detachment from a wall surface, e.g., using separate quantities, a wall surface adhesion quantity Fwv(k) of a low boiling point component and a wall surface adhesion quantity Fwp(k) of a high boiling point component at each time k, and to control an injected fuel quantity Fi(k) so that a fuel quantity Fc(k) of fuel flowing into the cylinder becomes a target value.