Abnormality detection apparatus and method for oil level sensor

An abnormality detection apparatus for detecting an abnormality of an oil level sensor having lower and upper oil level detectors includes: a recording portion that records the output of the upper oil level detector before the internal combustion engine is started; and a determining portion that determines that the upper oil level detector has an abnormality if the output of the lower oil level detector is indicating, after the start of the internal combustion engine, that the oil level is higher than the first reference oil level while the output of the upper oil level detector recorded by the recording portion is indicating that the oil level was lower than the second reference oil level before the start of the internal combustion engine.