PURPOSE: To prevent the torque of an engine from lowering, by computing the supply amount of fuel in accordance with the rotational speed of the engine, and then by supplying the above-mentioned amount of fuel into the engine when a change occurs such that an intake-air condition by one intake-air passage is turned into the other intake-condition by two intake-air passages.

CONSTITUTION: In an engine in which an intake-air control valve 4 controlled to be rotated by an actuator is disposed in a second one of first and second intake-air passages 1, 2 provided for every engine cylinder, on the left side of the communication part 3 between the first and second passages 1, 2, and a fuel injection valve 11 is disposed in the communication part 3, there is provided an intake-air condition change detecting means I for detecting such a change, under the control of the intake-air control valve 4, that a first intake-air condition by the first intake-air passage 1 along is turned into a second intake-air condition by both intake-air passages. Further, there is provided a fuel amount computing means III for computing the supply amount τof fuel in accordance with the output of a rotational speed detecting means II. Further, when the above-mentioned change of intake-air conditions is detected, a fuel supply means IV feeds the above-maintained amount τ of fuel into the fuel injection valve 11.