PURPOSE: To reduce tack on a resin surface, improve handleability and preservation stability in use as a single core wire and further handleability in post- working by irradiating optical fiber coated with a resin with ultraviolet rays in a low-oxygen atmosphere.

CONSTITUTION: The subject apparatus has a coating die 11 for coating optical fiber 10 with an ultraviolet curing type resin, an ultraviolet ray irradiator 13, a cylinder 14 connecting both and further a connecting means 15 for keeping the interior of the aforementioned cylinder 14 and the interior of the irradiator 13 in an atmosphere at ≤1% oxygen concentration. The connecting means 15 is provided with a device for feeding a gas, e.g. nitrogen gas without containing oxygen through the cylinder 14 and a feed port 16 and an oxygen concentration sensor 17. The outer peripheral surface of the optical fiber 10 is initially coated with the ultraviolet curing type resin and the surface of the coated optical fiber 12 is then irradiated with ultraviolet rays without contact with the outside air. Thereby, the objective optical fiber excellent in coating properties of a color ink and handleability both as a single core wire and in fusing connection in which dust hardly sticks to the surface is obtained.