PURPOSE: To achieve a high precision diagnosis using a simple configuration by allowing an EGR device to make self-diagnosis on the basis of whether the deviation of the measured rate of suction air flow from the rates of suction air flow determined in the EGR passage control conditions as opened and closed indicates the value corresponding to on/off of the exhaust gas feedback.

CONSTITUTION: While a car is running, its control unit 8 judges whether the situation lies within the self-diagnostic region (high-load, high revolving speed region) of an EGR device, and if yes, the rate of suction air flow QTN is calculated using a map, etc., on the basis of the opening TVO of a throttle valve 6 and the engine revolving speed N. Then a hot-wire flow meter 22 measures the actual rate of suction air flow QAFM, followed by calculation of the suction air rate-of-flow deviation ΔQ, and if an EGR control solenoid 9 is on, judgement is made whether the deviation ΔQ is over the specified value X determined by the fundamental fuel injection amount Tp etc. If judged as ΔQ<X, the EGR control solenoid 9 is judged to be in failure.