To reduce dispersion of the controlling center of the air-fuel ratio correction amount for the air-fuel ratio feedback control of an internal-combustion engine, improve the stability in controlling, and enhance the exhausting characteristicts of the engine.

An electronic control device (ECU) 30 calculates the air-fuel ratio feedback correction factor to repetitively perform the skip control and integral control so that the sensor voltage VO of an oxygen sensor 11 installed on the exhaust system 4 converges to the reference voltage and corrects the fuel injection amount using the obtained correction factor. The ECU 30 estimates the delay time from the fuel injection to the oxygen sensor 11 emitting the sensor voltage VO, and when the skip control is to be made, the air-fuel ratio feedback correction factor after skip is decided while the air-fuel ratio feedback correction factor calculated before the delay is used as reference.