A relative refractive index difference Δ1 between a center core region and a cladding layer is 0.30% to 0.35%, a relative refractive index difference Δ2 between an outer core layer and the cladding layer is −0.10% to −0.04%, and Δ1:Δ2 is 2.5:1 to 7.5:1. A diameter of the center core region is 9.0 μm to 10.5 μm, and a ratio of diameters of the center core region and the outer core layer is 0.20 to 0.35. A cutoff wavelength is 1310 nm or shorter, a zero dispersion wavelength is 1285 nm to 1345 nm, and at a wavelength of 1550 nm, an MFD is 10.5 μm or larger, a transmission loss is 0.185 dB/km or lower, and a bending loss is 15 dB/m or lower.