PURPOSE: To stabilize idling engine speed by making the differential term of a control gain determining means zero during a second defined term when judged to be in a first defined term after starting by a post-starting judging means.

CONSTITUTION: A control means 8 has an engine speed detecting means 15 for detecting the engine speed of an internal combustion engine 1, a post-starting judging means for judging whether the engine is in a first defined term after completing starting or after the defined term, and a target engine speed setting means for setting a target engine speed, and detects the deviation between an engine-speed detected value and a target engine speed to determine a control gain in response to the post-starting judging means. When judged to be in a first defined term after starting by the post-starting judging means, the differential term of a control gain determining means is made zero during a second defined term. Thereby, the lowering of controlling quantity of a control valve and the rise in engine speed at the time of shifting to an idling condition can be properly avoided.