An abnormality detection device for an air-fuel ratio detection device arranged downstream of a filter is equipped with an abnormality detection unit that detects an abnormality in the air-fuel ratio detection device based on output change characteristics of the air-fuel ratio detection device during fuel cutoff control for stopping the supply of fuel to a combustion chamber of an internal combustion engine, and a combustion determination unit that determines whether or not a combustion amount of particulate matter in a filter during fuel cutoff control is larger than a predetermined amount. The abnormality detection unit prohibits detection of an abnormality in the air-fuel ratio detection device when the combustion determination unit determines that the combustion amount is larger than the predetermined amount.