PURPOSE: To prevent EGR amount from fluctuation caused by change in pressure loss of exhaust gas in the heading device provided with a system in which fine grain of exhaust gas is processed with a collecting material, by enabling an EGR controlling valve to be feedback controlled in response to oxygen concentration in the upstream of the collecting material.

CONSTITUTION: In the heading device wherein a diaphragm system EGR controlling valve 23 is interposed in an EGR path 22 for circulating a portion of exhaust gas in an exhaust manifold 9 to a feed manifold, an oxygen concentration sensor 11 is provided right upstream of a trapper container 12 mounted on the downstream side of the exhaust manifold 9. The output signal of the sensor 11 is sent to the input of CPU 15 to feedback controll the opening of the EGR controlling valve 23 so that the oxygen concentration of exhaust gas reaches a predetermined value. Namely when pressure loss of exhaust gas upstream of the trapper container 12 is increased, the oxygen concentration is reduced, so that signals for interrupting a negative pressure path from CPU 15 to VSV 24 are generated to thereby block the transmission of negative pressure to EGR valve 23 and close the EGR path 22.