A temperature detecting element is fixed reliably at an accurate position to enable improvement in a rising characteristic of a temperature and high-accuracy temperature control. Provided is a temperature sensor including a temperature detecting element detecting a temperature in a branch tube branched from a main tube and a positioning supporting mechanism positioning and supporting the temperature detecting element. Tension is applied to a cord of the temperature detecting element. The positioning supporting mechanism is supported by the tensioned cord to position and support the temperature detecting element. The positioning supporting mechanism includes a supporting tube supporting the temperature detecting element, a positioning member supporting the supporting tube and fixed at a set position, and a tensioner applying tension to the cord of the temperature detecting element.