PURPOSE: To reduce volatile components remaining in a resin, by passing an optical fiber having a protective coating material coated on the surface thereof for a given period after the resin in the coating material starts curing reaction in an atmosphere under reduced pressure.

CONSTITUTION: An optical fiber preform 1 is melted and drawn while being heated to form an optical fiber 3. A liquid resin 4 of a protective coating material is then applied to the surface of the optical fiber 3. The resultant optical fiber 3 coated with the resin 4 is subsequently passed through a resin curing device 6 to cure the resin. The fiber is run through an atmosphere 7 under reduced pressure for a given time after the resin starts curing reaction. Thereby volatile components remaining in the coating material are reduced.