Abstract: An abnormality-detecting device for an exhaust gas component concentration sensor arranged in the exhaust system of an internal combustion engine detects abnormality of the exhaust gas component concentration sensor, based on an amount of change in an output from the exhaust gas component concentration sensor exhibited when a predetermined voltage is applied thereto. The abnormality-detecting device defers determination of abnormality of the exhaust gas component concentration sensor until the engine reaches a predetermined operating condition after the engine is started.