To detect a failure of a position contact outputting a contact signal, a change of a shift pattern defined by a combination of contact signals is monitored. Upon detection of the shift patterns belonging to a plurality of regions bridging a shift position corresponding to a selected position during an off period of the contact signal, a failure of the position contact is detected. As such, in a shift position sensor selecting a shift position by a combination of the contact signals from a plurality of position contacts, abnormality of the position contact can be detected reliably.