A temperature sensor (10) includes temperature detecting means and at least one of a catalyst and an adsorbent applied to the surface of the temperature detecting means. At least one of the catalyst and the adsorbent catalyzes an exothermic reaction of a reactant in gas on the temperature detecting means. A temperature that is increased by the exothermic reaction is detected by the temperature detecting means. The catalytic efficiency for the exothermic reaction of at least one of the catalyst and the adsorbent is reduced by sulfur poisoning. The temperature sensor (10) is disposed upstream of an exhaust purification system (30). Accordingly, it is determined that the temperature sensor is subjected to sulfur poisoning if the temperature detected by the temperature sensor is below a prescribed temperature.