A furnace for drawing an optical fiber includes a body having an upper and lower openings for supplying a preform and discharging a drawn optical fiber, a heating unit installed in the body for receiving and melting the preform, an atmosphere blocking tube installed to the lower opening for discharging the drawn optical fiber and blocking the optical fiber from the atmosphere, an upper introduction port formed at an upper portion of the body for introducing an inert gas toward the preform and partially discharged outside through a gap between the preform and the upper opening, a central and lower introduction ports formed at central and lower portions for introducing an inert gas into the body, a first flow guiding means for guiding the inert gas introduced through the central introduction port upward and then flowed down along a surface of the preform, and a second flow guiding means for guiding the inert gas introduced through the lower introduction port upward and then discharged outside through the atmosphere blocking tube along a surface of the drawn optical fiber.