PURPOSE: To eliminate the unstableness of an EGR rate and upgrade the operatability of an engine by providing hysteresis to the operating point of a control valve which can change the opening position step by step like an inlet throttle valve.

CONSTITUTION: The engine rotational speed N, is calculated by feeding the output of a rotary sensor 10 to a rotational speed calculation circuit 15, and fuel injection volume Q is calculated by supplying the output of a lift sensor 12, fitted with a fuel injection valve, to an injection volume calculation circuit 16. The engine rotary speed N and fuel injection volume Q are supplied to a primary function generator 17 and a secondary function generator 18 respectively, thereby obtaining a primary set value Q1 of injection volume, which shifts the opening position of an inlet throttle valve 6 from full open to half open in proportion to the rotary speed N, and a secondary set value Q2, which shifts the opening position of the inlet throttle valve from half open to full open. A signal representing the difference between the injection volume and set value is supplied to a hysteresis circle 21, so as to make ON-OFF control of the solenoid of a negative pressure control valve 7 for an EGR valve. The variation of the sensor characterstics is eliminated by the hysteresis circuit 21 and the EGR volume is stabilized.