An optical fiber includes a core, a depressed inner cladding surrounding the core, and an outer cladding surrounding the inner cladding, where a refractive index profile of the core includes an α power distribution in which an index α is 3.5 or more and 6 or less, a relative refractive index difference Δ− of the inner cladding with respect to the adding is set such that an absolute value |Δ−| thereof is 0.01% or more and 0.045% or less, a radius r1 of the core and an outer circumference radius r2 of the inner cladding are set such that a ratio r1/r2 thereof is 0.2 or more and 0.6 or less, a cable cutoff wavelength λcc of 22 m is 1260 nm or less, and a mode field diameter MFD at a wavelength of 1310 nm is 8.6 μm or more and 9.5 μm or less.