PURPOSE: To sense complete combustion at low revolving speed accurately by setting the starting time judgement speed for an internal-combustion engine to three different levels i.e., initial value, an intermediate value which is variable, and a higher value than the after-the-complete-combustion judgement speed.

CONSTITUTION: An initial value H1 (700rpm) to continue to be at a high level for preclusion of influence of the first combustion until the starter switch becomes out of effect is set in the starting time judgement speed NSTRT. A variable intermediate value H2 is provided, which applies after the starter switch becomes out of effect and decreases slowly. The a third value is provided, which receives the final level of said variable intermediate value H2 and which shall be higher than the after-the- complete-combustion judgement speed. The sinking rate of the intermediate value H2 shall be lower than the sinking rate of the revolving speed NE of the engine before complete combustion when the starter switch becomes out of effect. Thus the malfunction to judge the first combustion as a complete one at the starting time of an internal- combustion engine can be avoided, and complete combustion at low revolving speed lee sensed off surely.