PURPOSE: To set accurately an optical fiber into a coat, by producing a reinforcing member having a storing groove and putting the optical fiber and then a filler into the storing groove.

CONSTITUTION: The reinforced fibers 2 are supplied from a fiber feeder 1. The fiber 2 receives the supply of the thermosetting resin 3 from a resin impregnating machine 4 and then passes through the inside of a cylindrical heat molding machine 5 to be formed into a reinforced member 6 having a storing groove on its outer circumference. An optical fiber 9 is stored into the storing groove and moved toward the center hole of a butt strap 11. On the other hand, a fiber material 14 similar to the fiber 2 is led into a resin tank 18 and then impregnated with the liquid thermosetting resin 19. Thus a filler 12 is obtained. The filler 12 reaches the strap 11 and then goes into the storing groove of the member 6 to block the groove.