The present invention relates to an exhaust gas sensor abnormality diagnostic device, providing an exhaust gas sensor abnormality diagnostic device being able to diagnose high-precision abnormity caused by exhaust sensor element breakage. The exhaust gas sensor abnormality diagnostic device comprises an exhaust sensor, a judgment means that judges whether execution conditions are established for making an abnormality diagnosis of element breakage in the exhaust gas sensor., and an abnormality diagnosis means that makes the abnormality diagnosis in accordance with an output signal generated bythe exhaust gas sensor. The judgment means judges that the execution conditions are established when the air/fuel ratio of exhaust gas is in rarity period. Further, when the accumulated value of intake air amounts of an internal combustion engine is bigger than predetermined value, the judgment means judges that the execution conditions are established. The abnormality diagnosis means cancels theestablishment of the execution conditions when an intake air amount of the internal combustion engine remains less than a predetermined value for a predetermined period of time.