An abnormality detecting device of an internal combustion engine according to the present invention includes a sensor nick abnormality detecting unit configured to detect a nick abnormality in a detecting element of a downstream side sensor which is provided in a downstream side of an exhaust gas purifying catalyst in an exhaust passage and generates an output corresponding to an oxygen concentration in exhaust gas, on the basis of a matter that a distribution of an output of the downstream side sensor is biased to an area in which the air-fuel ratio is leaner than a theoretical air-fuel ratio, and an inhibiting unit configured to inhibit detection of the nick abnormality of the detecting element by the sensor nick abnormality detecting unit in the case that an intake air amount exceeds a predetermined amount.