A control device for an internal combustion engine performs feedback control so that the air-fuel ratio of the exhaust gas flowing into an exhaust purification catalyst becomes a target air-fuel ratio and switches the target air-fuel ratio to lean when an output air-fuel ratio of a downstream side air-fuel ratio sensor is judged rich and switches the target air-fuel ratio to rich when an output air-fuel ratio of the downstream side air-fuel ratio sensor is judged lean. The control device judges that the downstream side air-fuel ratio sensor has not become abnormal when the value of the excess/deficiency parameter from when switching the target air-fuel ratio to lean or rich to when the output air-fuel ratio of the downstream side air-fuel ratio sensor is judged rich or lean is larger than a predetermined limit value.