According to an aspect of the present invention, there is provided an abnormality judgment device including: a change amount calculator configured to calculate a change amount between currently-obtained and previously-obtained steering angles; a storage section configured to store a threshold value; a reference setting section configured to set a reference steering angle; an incrementing section configured to continue gradually incrementing the threshold value after the change amount exceeds the threshold value, for a judgment time; a deviation comparator configured to compare an absolute deviation between the currently-obtained steering angle and the reference steering angle with the threshold value, and to count a counter when the absolute deviation exceeds the threshold value; and a judgment section configured to judge that the steering angle sensor is abnormal when the counter reaches a predetermined value.