State determining apparatus for humidity sensor

A state determination apparatus for a humidity sensor (22) is provided for accurately determining the state of the humidity sensor, including the responsibility, from a result detected by the sensor Itself. The state determining apparatus is configured to determine a humidity sensor (22) arranged in an exhaust system (2) of an internal combustion engine (1) for detecting a humidity within an exhaust pipe. The apparatus comprises an ECU (25) which determines whether or not the internal combustion engine (1) is in a predetermined operating condition, calculates a change state parameter indicative of a change state of a value detected by the humidity sensor (22) based on the detected value of the humidity sensor detected when the internal combustion engine (1) is in the predetermined operating condition, and determines the state of the humidity sensor in accordance with the calculated change state parameter.