To decrease the number of component members, to facilitate production and to enable rapid assembly.

The conversion structure 10 of the multifiber-to-fiber cord conversion part is at least a multifiber coated fiber ribbon on the multifiber side in the multifiber-to-fiber cord conversion part for separating the optical fiber multifiber coated fiber ribbon to fiber cords. The multifiber coated fiber ribbon is separated to a plurality of fiber-cord coated optical fibers. The fiber cord side is constituted by assembling at the fiber-cord coated optical fibers and a plurality of fiber cord reinforcing cords 5 consisting of tubes at least protecting these coated fibers. The multifiber-to-fiber cord conversion part exists in a hollow member 12 and a resin 13 is packed into this hollow member to fix the conversion part to the hollow member.