PURPOSE: To obtain the titled fiber having superior strength with high work efficiency by coating an ultraviolet-curing resin on a glass fiber for optical transmission, further coating a thermoplastic resin by extrusion before curing the ultraviolet-curing resin, and curing the ultraviolet-curing resin.

CONSTITUTION: A glass base material for an optical fiber is drawn, and the resulting optical fiber is subjected to primary coating B. The coated optical fiber A is supplied from a supplier 12 to the crosshead 14 of an extruder, and an ultraviolet-curing resin C is fed from a resin feeder 13 and coated on the fiber A. Before curing the resin C, a thermoplastic resin D is coated by extrusion, and the fiber A is introduced into a cooling trough 18, where the resin D is cooled and molded. The ultraviolet-curing resin layer C is then cured with an ultraviolet-curing device 19. The desired glass fiber for optical transmission covered successively with a primary coating, an ultraviolet-curing resin layer and a thermoplastic resin layer is obtd.