PURPOSE: To prevent the leaning of mixture at the time of look-up operation, and to prevent the occurrence of surging, by controlling in such a way that the fuel supply quantity decreasing action by means of a mixture leaning means is delayed extending for a prescribed time from the time when the engine has shifted to a prescribed low load operation.

CONSTITUTION: In an engine 1 equipped with an automatic transmission fitted with a torque converter 15, in which the lock-up mechanism 15a of the torque converter 15 is operated at the time when a vehicle is decelerated, the fuel consumption rate is enhanced by decreasing the fuel injection quantity from a fuel injection valve 6 so as to lean the mixture by means of an ECU 5 when the engine 1 is operated in a prescribed low load condition. In such a fuel supply control device, a delaying means by which the fuel supply quantity decreasing action for leaning the mixture is delayed extending for a prescribed time from the time when the engine has shifted to the above prescribed low load operation is provided in the ECU 5. Thus, the leaning of mixture at the time when the lock-up mechanism 15a is operated due to the deceleration of the vehicle can be prevented, and the occurrence of surging can be prevented.