PURPOSE: To improve mixing ratio controllability in a phase control of a basic fuel injection amount by correcting a control amount of weighting according to a change of an air flow charged in a cylinder of an engine or stopping weighted average processing when the change of the air flow is less than a predetermined value.

CONSTITUTION: A basic fuel supply amount is set by a means A based on a quantity of state of an intake air, this basic fuel supply amount is weighted- averaged by a control amount for weighting determined by an engine revolution speed and an opening area of an intake system, and the weighted average basic fuel supply amount is calculated by a means B. A fuel supply amount is set by a means C based on the basic fuel supply amount or the weighted average basic fuel supply amount, and a fuel supply means D is controlled by a means E based on this fuel supply amount. In the above fuel supply control device, the control amount for weighting is corrected by a means F according to a change of an air flow charged in a cylinder of an engine. When the change of the air flow is less than a predetermined value the weighted average processing is stopped by a means G.