PURPOSE: To permit to stop a feedback control under the specified condition of the engine with a simple circuit by selecting an exhaust gas sensor signal or an engine specified condition detecting signal.

CONSTITUTION: The output 15 of the exhaust gas sensor 5 of an engine 1 operates the solenoid valve 6 of a carburettor 4 through an OR circuit 8, an integral circuit 19, a limit circuit 20, a gate circuit 21 and an output circuit 22 and the feedback control is effected upon the normal operation of the engine. On the other hand, one of signals LM, indicating the load condition of the engine upon a light load except idling of the engine or a high load, is inputted into the OR circuit 18 by the signals of a suction pipe vacuum switch 11, a cooling water temperature sensor, a throttle switch 13, an ignition coil, an output signal of an engine revolving number sensor 14 or the like. In this case, the signal is inputted regardless of the output of an exhaust gas sensor and an integral signal is outputted into the direction of diluting it, thus, an open control is effected.