To prevent worsening of operability and to draw out catalytic conversion efficiency to a maximum limit by a method wherein generating torque of an internal combustion engine is compensated by a trigger signal by which an air-fuel ratio is changed to the rich side or the lean side.

Operation state information 20a is transmitted to a trigger signal generating means 22 and in a case of being decided that the trigger signal may be generated, a time distance of trigger signal generation is decided according to the operation state information 20a and catalytic conversion detecting information 29a and a trigger signal 22a is generated. It is decided by an air-fuel ratio regulating means 24 to which extent amplitude of an air-fuel ratio of feed air-fuel mixture fed to an internal combustion engine provided in synchronism with a generating trigger signal 22a is determined. Meanwhile, information indicating that an air-fuel ratio of feed air-fuel mixture is switched to the rich side or the lean side is transmitted to a torque correction direction deciding means 23 and it is decided whether generating torque is decreased or increased. In a case of torque being corrected by, for example, an ignition timing, decided angle of lag and angle of lead information is transmitted to a torque correction amount deciding means 25 in synchronism with a trigger signal, and it is decided to what extent a delay or advance is executed.