PURPOSE:To allow the efficient transfer of the light in not only a visible region but a near IR region as well by forming a specific copolymer as a core and a specific polymer as a clad. CONSTITUTION:The polymer of 30 to 50wt.% vinylidene fluoride and 15 to 25wt.% at least one kind of the monomers selected from hexafluoropropylene, trifluoroethylene, perfluoroalkyl vinyl ether, and hexafluoracetone is used as the core. The polymer which is the copolymer of perfluoro (2, 2-dimethyl-1, 3-dioxol) and at least one piece of other ethylenic unsatd. monomer and has the refractive index lower than the refractive index of the polymer for forming the fiber material is used as the clad. The all plastic optical fiber formed of these materials is the lower ratio of the C-H bonds per the molecule of the fiber material and has the extremely low water absorptivity and, therefore, the increase in the transmission loss by absorption of water is obviated and the transmission losses in not only the visible region but the near IR region are decreased.