PURPOSE: To improve the combustibility when an engine is cooled by opening and closing a suction control valve in consideration of the warming-up degree of an internal-conbustion engine.

CONSTITUTION: When the temperature of cooling water in an engine is under a fixed level, a negative pressure is supplied to a diaphragm chamber 23 without reference to the operating condition of the engine, and a valve element 17 is positioned at a perfectly closed position to close a straight passage 14. All air- fuel mixture is conducted through a helical passage 13 to be introduced into a combustion chamber 2, and a strong swirl is generated in the combustion chamber. When the temperature of cooling water of the engine is over a fixed level, the increase of the amount of suction air over a fixed value introduces atmospheric pressure into the diaphragm chamber 23, and the valve element is positioned at a fully opened position to open the straight passage 14.