An air-fuel ratio controller of an internal combustion engine which can perform air-fuel ratio control with characteristics suitable for each operation range when the air-fuel ratio control of the internal combustion engine is performed, and is directed particularly to improve control response and to eliminate an erroneous operation. When a fuel correction quantity is set in accordance with the difference Δ(A/F) between a measured air-fuel ratio (A/F) i and a target air-fuel ratio (A/F) OBJ , the controller of this invention is designed so that the fuel correction quantity is limited in accordance with limit values K LMIN , K LMAX , K RMIN , K RMAX corresponding to the target air-fuel ratio. Therefore, the engine which is subjected to fuel supply control by the target fuel quantity T INJ based on this fuel correction quantity is operated with optimum characteristics for each operation range, can particularly improve response, can reliably reduce a knock in a knock occurrence zone, can prevent engine trouble and breakage and exhaust gas deterioration resulting from erroneous operation during the air-fuel ratio control, and can prevent stalling of the engine.