PURPOSE: To improve the running performance of an engine even upon speed change, particularly to improve the response and acceleration abilities of the engine, and as well to reduce the rate of black smoke, etc. contained in exhaust gas, by returning and recirculating exhaust gas into an intake-air system in accordance with the operating condition of the engine, and as well by rapidly restraining or stopping exhaust gas circulation.

CONSTITUTION: A control unit 100 delivers a fuel injection timing control signal Ct to a valve 25 and an exhaust gas recirculation control signal Ce to a vacuum pressure control valve 41 in accordance with various detection signals which indicate the operating condition of the engine. Further, the range in which exhaust gas recirculation is carried out is limited to a range in which an accelerator is depressed in a certain amount and the rotational speed of the engine has a certain value. Further upon exhaust gas recirculation a vacuum supply port 42 is communicated with a vacuum port 43 and an atmospheric air suction port 46, alternately at a time rate in accordance with the duty ratio of the signal Ce. The larger the duty ratio, the more the effective opening area of a port 32 increases so that the amount of exhaust gas recirculation increases. Meanwhile, in a speed shift phase by a speed change gear unit exhaust gas recirculation is forced to be stopped for a predetermined period.