A thermocouple includes: a temperature measuring portion configured to measure an internal temperature of a reaction tube; a main body portion provided therein with a wire which constitutes the temperature measuring portion; and a cushioning portion attached to the main body portion at least in the vicinity of the temperature measuring portion, wherein the thermocouple is fixed to an outer surface of the reaction tube in a state in which the thermocouple makes contact with the reaction tube through the cushioning portion.