PURPOSE: To prevent the hunting by releasing the function of fuel shut-off temporarily when the hunting is caused in full closing the throttle valve due to an abnormal increase of idling of the engine in the mechanism wherein the fuel cost is economized by stopping the fuel injection when the speed is decelerated.

CONSTITUTION: Output as set values A, B, which vary with water temperature, is fed to the comparators 8, 9 through the function generator 6, 7, and output of the fuel injection control circuit 2 is also fed to said comparators 8, 9 through the switch 4, which is closed when the idle switch 3 is "on", and the F-V converter 5. When the Q-output of FF10, which accepts the outputs of comparators 8, 9, is "1", that is, when the number of rotation is greater than a set value during a reducing operation, the switch 13 is turned off to stop the actions of all the fuel injection valves 22, 23, 26, 27, and a means A that releases said fuel shut-off function only for a fixed time when the hunting is detected is provided.