A correction device for an air/fuel ratio sensor in the present invention has air/fuel ratio control means for controlling an air/fuel ratio of an exhaust gas on the upstream side from a catalyst (6) installed in an exhaust passage of an internal combustion engine to switch between a rich air/fuel ratio which is richer and a lean air/fuel ratio which is leaner than a stoichiometric air/fuel ratio, and an air/fuel ratio sensor (12) issuing an output according to the air/fuel ratio of an exhaust gas on the downstream from the catalyst (6) of the exhaust passage. Moreover, correction coefficient calculating means for calculating a correction coefficient for correcting an output of the air/fuel ratio sensor (12) in accordance with a difference between the output of the air/fuel ratio sensor (12) during a predetermined period during which the output of the air/fuel ratio sensor (12) installed on the downstream from the catalyst (6) is equilibrated during air/fuel ratio control by the air/fuel ratio control means, and a reference output corresponding to a stoichiometric air/fuel ratio, is provided.