PURPOSE: To coat an optical fiber to a uniform outside diameter by disposing coaxially a resin vessel and a nozzle and coating the optical fiber moving coaxially while rotating the nozzle.

CONSTITUTION: An optical fiber 15 to be coated is first put into a vessel 12 from the upper opening thereof then a resin 14 is run into the vessel 12. When a motor 18 is started, a nozzle 13 is rotated via a gear 18 and the resin 14 sticks to the fiber 15 which moves toward α direction while the fiber is taken up on a winder below the nozzle 13. As the nozzle 13 is rotated, the circumferential resistance and centripetal force act on the fiber 15 and therefore the wettability of the resin 4 with the fiber surface is stabilized and the coating is made uniform as shown by a broken line A. The fluctuation in the outside diameter of the coating is decreased from ±5μm to ±2μm as compared to the conventional technique.