PURPOSE: To obtain the titled optical fiber drawing furnace wherein the consumption of a furnace core tube material and heating element is prevented and an excellent optical fiber can be obtained by using the furnace core tube made of zirconia in the optical fiber drawing furnace.

CONSTITUTION: A cylinderical carbon heater 2 is arranged at the inside of the furnace body 1 of an optical fiber drawing furnace, and a heat insulating material 4 is arranged around the heater. A furnace core tube 3 made of zirconia is provided at the inside of the heater 2, and the atmospheres on the heater 2 side and at the inside of the tube 3 are isolated by gas seals 5a and 5b. Then a specified atmospheric gas is allowed to flow into the inside of the tube 3 from the atmospheric gas inlet 6 provided at the lower part of the furnace body 1, and a fiber 8 is drawn while controlling the heating atmosphere of an optical fiber base material 7 consisting essentially of quartz glass. Consequently, since the heating atmosphere of the base material 7 can also be composed of an oxygen atmosphere as well as an inert atmoshere along with said characteristics, the generation of cracks on the surface of the fiber 8 in drawing is prevented, and a long-sized high-strength fiber can be obtained.