An air-fuel ratio control device for an internal combustion engine controls an air-fuel ratio to the lean side rather than to a stoichiometric air-fuel ratio by the use of a factor determined in accordance with inlet pipe pressure and engine speed. A throttle opening degree sensor is provided to detect a degree of throttle opening, and on the basis of the degree of throttle opening, the factor determined in accordance with the inlet pipe pressure and the engine speed is corrected in a high load range of the engine. Since the output of the throttle opening degree sensor in the high load range of the engine is more accurate than the output of a pressure sensor for detecting the inlet pipe pressure, the air-fuel ratio can be controlled accurately in the high load range by correcting the factor in accordance with the degree of throttle opening.