PURPOSE: To obtain temp. monitoring apparatus capable of corresponding to sample temp. in reaction tube vessel, by isolating a temp. sensor from reaction tube vessel, further setting it in a vessel having equal characteristic to heat ray transmission characteristic of reaction tube vessel and reduced inner pat pressure.
CONSTITUTION: In the titled apparatus in which inside of a reaction furnace 1 is evacuated by a vacuum pump 5 connected to an exhausting tube 4 and a sample 2 arranged therein is heated from outer part by a lamp heater 3, a temp. measuring instrument 6 such as thermocouple, at least a temp. sensor 7 is inserted in a vessel 8 made of material having substantially almost equal heat ray transmissivity to that of heat ray transmitting part material of the furnace 1, and inside pressure of the vessel 8 is reduced by an evacuating pump 10 connected to an exhausting tube 9. In this way, correspondence in temps. of the sensor 7 and the sample 2 becomes satisfactory, and controllability of sample temp. is improved even raising or lowering temp. of the sample 2.