PURPOSE: To provide a fiber drawing furnace equipping a furnace core tube for supplying a preform, a heater surrounding the furnace core tube and an upper chamber linked to the upper end of the furnace core tube, capable of suppressing the convection of an inert gas between the neighborhood of the furnace core tube and the upper end part of the upper chamber by keeping the temperature at the upper end part of the upper chamber constant by heating.

CONSTITUTION: The method for fiber drawing of an optical fiber is constituted by delivering a preform for the optical fiber 15 connected to the lower end of a supporting rod 18 successively to the side of a furnace core tube 14 accompanying to the fiber drawing, supplying an inert gas to the upper chamber 24 of the furnace core tube 14 through a gas supplying pipe 28, a gas introducing cylinder 27 and a gas introducing port 29, installing a heater 34 for keeping the temperature of the upper chamber 24, and controlling it with a regulating device 35 and a temperature sensor 34. On the verge of the completion of the fiber drawing work of the preform for the optical fiber 15, the temperature at the upper end part of the upper chamber 24 is lowered to ≤100°C in the case of not using the heater 34 for keeping the temperature, but by keeping the temperature at 100-700°C with installing the heater 34 for keeping the temperature, the increase in the difference of a temperature of the inert gas in the inside of the furnace core tube is prevented and a good quality product with less line diameter variations can by stably produced.