To quantitatively judge the degree of abnormality while detecting abnormality generated in a sensor at a high accuracy.

The sensor abnormality detector detects abnormality generated in a sensor based on a difference between a detection status value of a vehicle detected by the sensor and an estimated status value estimated by an observer corresponding to a dynamic model of the vehicle. The observer, a residue computing part and a degree of abnormality converting part are prepared in three sets to compute two degrees of abnormality each for three types of sensors while a model of sensor abnormality incorporated into each of the observers is built individually in a different combination. Individual comparison processing parts compare two degrees of abnormality obtained from a certain sensor and an abnormality judging part judges the abnormality of the sensor based on the results of comparison.