PURPOSE: To perform such a trouble detection that is high in reliability by operating a secondary air feeder after completion of the warm-up of an internal combustion engine for the trouble detection, and regulating an air-fuel ratio in an inlet system so as to make the exhaust air-fuel ratio become rich if the secondary air feeder goes wrong.

CONSTITUTION: At time of driving an internal combustion engine M1, when a secondary air control means M8 judges it to be a special driving state, for example, reduced speed driving on the basis of detection of a driving state detecting means M7, it controls a secondary air feeder M3, feeding an exhaust system M2 with secondary air. At this time, a fuel control means M9 controls a fuel supply means M6 to regulate an air-fuel ratio in an inlet system M5 so as to make an exhaust air-fuel ratio become lean if the secondary air feeder M3 is normal but rich if something is wrong in it, respectively, thereby feeding the inlet system M5 with fuel. A trouble judging means M10 judges to be something wrong in the secondary air feeder M3 at a time when it judges that the detected value of an exhaust air-fuel ratio detecting means M4 is rich.