To execute both feedback control and learning control in such a way that the revolving speed will be a target idle revolving speed at the time of idling, and determine a learning value while the period of purging is being sufficiently maintained when vaporized fuel is purged.

The opening of a bypass passage 8 bypassing a throttle valve 7, is adjusted by an ISC valve 9. The ISC valve 9 is controlled by means of feedback and means of learning in such a way that the revolving speed of an engine is turned out a target idle revolving speed at the time of idling. A feedback control valve is determined based on the amount of feedback correction. For the period of time since idle judgement has been made, a purging valve 36 is opened, vaporized fuel from a fuel tank 31 is purged to an intake passage 2, and no decision of a leaning value is made at this time. When the aforesaid specified period of time has elapsed, the leaning value is then decided, however, no purging of vaporized fuel is made at this time. When the learning value is thereby determined, for example, for the period of time until an automatic transmission is turned out to be at a D range position, vaporized fuel is thereby purged again.