PURPOSE: To measure easily and surely the temp. (distribution) of the wall surface of a coke oven, by using a cooling pipe transmitting the thermal radiant light of the wall of the oven through glass fiber internally provided.

CONSTITUTION: In a cooling pipe 2 where a heat insulating material 8 is provided on the outer periphery of the outer tube 8 of a metallic double tube (inner tube 7, outer tube 8), a side view hole 1 is provided at the bottom thereof and a glass fiber 3 is internally provided (numerals 9, 10 being inlet and outlet for cooling air). Coal D introduced into a coking chamber B is dry-distilled by indirectly heating it through the wall C of the oven by the combustion of a heating gas in a combustion chamber A, thus obtaining coke. Said cooling pipe 2 is inserted into the combustion chamber A and thermal radiant light radiated from the wall C of the oven is received through the side sight hole 1 (numeral 11: glass-paned window) and guided through a prism 12, a lens 13 and an optical fiber 3 to a photoelectric converter 4. The temp. of the wall C of the oven is measured by using the obtained electric signal.