A system for detecting the abnormality of a steering angle sensor comprises a steering angle sensor for detecting the steering angle of a wheel of a vehicle to be steered, a reference motional parameter determining apparatus for determining a reference value of a vehicle motional parameter on the basis of the steering angle, a motional parameter detector apparatus for detecting a vehicle motional parameter indicative of the same physical quantity as the reference motional parameter, and an abnormality judging apparatus for judging the abnormality of the steering angle sensor by use of the reference motional parameter and the vehicle motional parameter. It is possible to reliably and promptly detect the abnormality of the steering angle sensor. Further, abnormality judging conditions are stabilized by a delaying timer adapted to start the judgement by the abnormality judging apparatus at a given interval after satisfaction of the abnormality judging conditions, and this contributes to a further correct judgement.