A temperature sensor includes a pair of thermocouple wires, a temperature measuring junction formed by joining tip ends of the pair of thermocouple wires together, an outer tube having a tip end provided with a tip end cover in which the temperature measuring junction is held, an insulator insulating the pair of thermocouple wires from the outer tube, and a glass seal filled in a base end of the outer tube to seal the outer tube from inside thereof. The glass seal contains bubbles which are independent of each other.