An exhaust gas purifying apparatus provides a reflux pipe for connecting an intake pipe to an exhaust pipe and an EGR valve disposed in the reflux pipe for adjusting a flow rate of the exhaust gas flowing through the reflux pipe. A nitrogen oxide purifying catalyst section is formed by a brown miralite type composite oxide. A pair of electrodes are provided on the vicinity of the opposite ends of the purifying catalyst section. A conductivity measuring section measures conductivity of a nitrogen oxide catalyst of the nitrogen oxide purifying catalyst section through the electrodes. A control section controls an opening degree of the EGR valve on the basis of engine rpm, engine load and the conductivity measured in the conductivity measuring section.