PURPOSE: To enable to start engine promptly, by connecting an air intake passage to the intake manifold, providing in the said passage a suction valve which is opened and closed intermittently in association with operation of a starter switch, and thereby correcting the air-fuel ratio at a proper value at the time of starting of engine under high-temperature.

CONSTITUTION: When a starter switch is turned on, switch 24 is resultantly turned on. Here, if temperature of engine is high and evaporation gas tends to be collected in intake manifold 1, temperature switch 25 is turned on and current is passed to interrupting circuit 11. As the result, capacitor 12 is charged gradually, and when anode potential becomes higher than a certain value determined by resistances 19, 20, PUT14 is turned off and transistor 15 is turned on, so that suction valve 9 is driven by solenoid 10. In the above arrangement, since solenoid 10 is energized intermittently at a predetermined frequency, fresh air is supplied to intake manifold 1 from suction valve 9 intermittently, so that required effects can be attained.