Production of multicore type optical fiber

PURPOSE:To readily manufacture the multicore type optical fiber having guide holes, etc. by melt-elongating the multirods having holes comprising bundling performs together with hollow interpolation pipes and melt-integrating these through heating. CONSTITUTION:Preform rods 3 are bundled together with the hollow interpolation pipes 4... of the same material as that of the rods 3, in a sheath pipe 5. When the pipe 4 is heated while the pressure therein is being increased or decreased, the outside circumferential part is melt-integrated and become the multirods formed by the holes 10..., core layers 1..., clads 2'. When the multirods are heated and elongated, the multicore type optical fiber provided with guide holes 14 or guide grooves 14' is readily manufactured.