An air-fuel ratio control apparatus for an internal combustion engine, comprising: an air-fuel ratio adjustment mechanism for adjusting an air-fuel ratio of the internal combustion engine; exhaust gas air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas; an ammonia sensor disposed in an exhaust system of the internal combustion engine; a catalyst so disposed in the exhaust system as to be located upstream of the ammonia sensor; an oxygen sensor disposed downstream of the catalyst; first feedback means for subjecting the air-fuel ratio adjustment mechanism to first feedback control such that the air-fuel ratio of exhaust gas becomes close to a target air-fuel ratio in a neighborhood of a stoichiometric air-fuel ratio; and second feedback means for subjecting the air-fuel ratio adjustment mechanism to second feedback control based on an output value of the ammonia sensor; third feedback means for subjecting the air-fuel ratio adjustment mechanism to second feedback control based on output values of the ammonia sensor and the oxygen sensor or an output value of the oxygen sensor; and second feedback selection means for selectively actuating the second feedback means and the third feedback means, wherein the exhaust gas air-fuel ratio detection means is equipped with an air-fuel ratio sensor disposed upstream of the catalyst, and the first feedback means performs the first feedback control on a basis of an output of the air-fuel ratio sensor, characterized by operation state detection means for detecting an operation state of the internal combustion engine, wherein the second feedback selection means selects the second feedback means as actuation means under fulfillment of a high-load operation condition, and selects the third feedback means as actuation means under fulfillment of a low-load operation condition. an air-fuel ratio adjustment mechanism for adjusting an air-fuel ratio of the internal combustion engine; exhaust gas air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas; an ammonia sensor disposed in an exhaust system of the internal combustion engine; a catalyst so disposed in the exhaust system as to be located upstream of the ammonia sensor; an oxygen sensor disposed downstream of the catalyst; first feedback means for subjecting the air-fuel ratio adjustment mechanism to first feedback control such that the air-fuel ratio of exhaust gas becomes close to a target air-fuel ratio in a neighborhood of a stoichiometric air-fuel ratio; and second feedback means for subjecting the air-fuel ratio adjustment mechanism to second feedback control based on an output value of the ammonia sensor; third feedback means for subjecting the air-fuel ratio adjustment mechanism to second feedback control based on output values of the ammonia sensor and the oxygen sensor or an output value of the oxygen sensor; and second feedback selection means for selectively actuating the second feedback means and the third feedback means, wherein the exhaust gas air-fuel ratio detection means is equipped with an air-fuel ratio sensor disposed upstream of the catalyst, and the first feedback means performs the first feedback control on a basis of an output of the air-fuel ratio sensor, characterized by operation state detection means for detecting an operation state of the internal combustion engine, wherein the second feedback selection means selects the second feedback means as actuation means under fulfillment of a high-load operation condition, and selects the third feedback means as actuation means under fulfillment of a low-load operation condition.