A thermometer comprising: a thermocouple having a pair of wires (16, 18), a temperature measuring junction between the wires (16, 18), and an insulator covering the wires (16, 18); a first protection tube surrounding the wires (16, 18), the temperature measuring junction, and the insulator of the thermocouple, said first protection tube being at least partially spaced apart from the wires (16, 18), the temperature measuring junction, and the insulator of the thermocouple; a second protection tube surrounding the first protection tube, said second protection tube being at least partially spaced apart from the first protection tube, and a third protection tube located outside the first protection tube and inside the second protection tube and surrounding the first protection tube, said third protection tube being at least partially spaced apart from the first protection tube and the second protection tube by a space provided between the first protection tube and the third protection tube and a space provided between the second protection tube and the third protection tube, wherein the first protection tube contains any one of Mo, W, Ta, and Ir, the second protection tube contains any one of graphite, C/C composite, glassy carbon, SiC, and BN, and the third protection tube contains any one of Mo, W, Ta, Nb, and Ir, or wherein the first protection tube contains any one of Mo, W, Ta, and Ir, the second protection tube contains any one of graphite, C/C composite, glassy carbon, SiC, BN, Al 2 O 3, vitreous carbon, pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, and PBN, and the third protection tube contains any one of Mo, W, Ta, Nb, Ir, graphite, C/C composite, SiC, glassy carbon, vitreous carbon, pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, BN, and PBN, or wherein the first protection tube contains any one of Al 2 O 3, MgO, CaO, BeO, ZrO 2, and HfO 2, the second protection tube contains any one of graphite, C/C composite, glassy carbon, SiC, and BN, and the third protection tube contains any one of Mo, W, Ta, Nb, and Ir, or wherein the first protection tube contains any one of Al 2 O 3, MgO, CaO, BeO, ZrO 2, and HfO 2, the second protection tube contains any one of graphite, C/C composite, glassy carbon, SiC, BN, Al 2 O 3, vitreous carbon, pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, and PBN, and the third protection tube contains any one of Mo, W, Ta, Nb, Ir, graphite, C/C composite, SiC, glassy carbon, vitreous carbon, pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, BN, and PBN. a thermocouple having a pair of wires (16, 18), a temperature measuring junction between the wires (16, 18), and an insulator covering the wires (16, 18); a first protection tube surrounding the wires (16, 18), the temperature measuring junction, and the insulator of the thermocouple, said first protection tube being at least partially spaced apart from the wires (16, 18), the temperature measuring junction, and the insulator of the thermocouple; a second protection tube surrounding the first protection tube, said second protection tube being at least partially spaced apart from the first protection tube, and a third protection tube located outside the first protection tube and inside the second protection tube and surrounding the first protection tube, said third protection tube being at least partially spaced apart from the first protection tube and the second protection tube by a space provided between the first protection tube and the third protection tube and a space provided between the second protection tube and the third protection tube,