PURPOSE: To obtain the title optical fiber having a low transmission loss by spinning the core fiber of fluoride glass, coating a fluororesin thereon, and keeping the core fiber in a vacuum to prevent the mismatching at the core-clad interface and to prevent the deposition of moisture.

CONSTITUTION: The fluoride glass 10 of ZrF4, BaF2, etc., is heated and melted by a heater 12 is a glass vessel 11. The melt is spun into a core glass fiber 21, and the fiber 21 is passed through the fluororesin 13 heated and melted by a heater 15 in a resin vessel 14. As a result, an optical fiber 5 consisting of the core fiber 21 and the molten fluororesin 13 coated thereon is obtained, and then wound on a drum 7 through a capstan 6. In the production of the optical fiber 5, the core fiber 21 passing from the spinning stage to the fluororesin coating stage is passed through the inside of a vacuum chamber 16 provided with a vacuum pump 17 and kept at a vacuum. By this method, the mismatching at the interface between the core and the clad is reduced, and the deposition of moisture on the core fiber 21 is controlled.