A sensor apparatus of the present invention includes a first output terminal for outputting a sense signal, and a failure diagnosis circuit for determining whether a failure diagnosis object section is normal or abnormal, to output a failure detection signal from a second output terminal in the case of determining abnormality. The time required for an output concerning the failure detection signal from the failure diagnosis object section to reach the second output terminal is shorter than the time required for an output concerning the sense signal from the failure diagnosis object section to reach the first output terminal, thus leading to improvement in reliability under abnormal condition.