A cladding 12 of a photonic crystal fiber 10 has first to fourth air hole layers 15 to 18 formed around a core 11 one after another in the radial direction of the fiber. In forming the fiber, assuming that air holes 12a constituting the first air hole layer 15 have a diameter d1, at least one of air holes 12a constituting the second to fourth air hole layers 16 to 18 is formed in a smaller diameter d2 than the diameter d1.