PURPOSE: To secure an exhaust recirculation quantity suitable to an altitude mixture position in an accurate manner, by detecting a combustion light inside a cylinder, and according to the intensity of the combustion light, controlling the exhaust recirculation quantity for the purpose of adjustment.

CONSTITUTION: In time of engine operation, at an electronic control circuit (ECU) 20, first a fundamental exhaust recirculation quantity is found on the basis of each detection signal of an engine speed sensor 35 and an accelerator opening sensor 42a, namely, engine speed and engine load. Then, the intensity of a combustion light is detected from an output signal out of a light detection circuit 36b of a flame sensor 36 installed with the tip end of an optical fiber 36a being exposed inside an auxiliary chamber 23 installed in a cylinder head 24 of an engine 21. Next, on the basis of the intensity of the combustion light, the said fundamental exhaust recirculation quantity is compensated, and according to the reciculation quantity after compensation, a solenoid type suction pressure control valve 61 is controlled, regulating feed suction pressure to an exhaust gas circulation (EGR) control valve 29, thus the opening of the said valve 29 is controlled.