A detection unit has a rotation angle sensor including at least three detection elements detecting a change of physical quantity and outputting angle signals respectively corresponding to detection values of the respective detection elements. The detection unit also has a controller including an abnormality monitor monitoring the angle signals and identifying the respective angle signals either as a normal signal or an abnormal signal. The controller either outputs a value corresponding to at least one of two normal signals when two or more normal signals are identified or stops output regarding the detection signal when two or more normal signals are not identified.