An optical fiber includes a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding. A mean relative refractive index difference Δ1 of the core, a mean relative refractive index difference Δ2 of the inner cladding, and a mean relative refractive index difference Δ3 of the outer cladding satisfy a relationship of Δ1>Δ3≥Δ2. A ratio r2/r1 of an inner cladding radius r2 to a core radius r1 is 4.5 or higher and 5.5 or lower. A minimum value Δmin of a relative refractive index difference is −0.030% or higher and −0.010% or lower. A radius rmin at which the relative refractive index difference is the minimum value Δmin satisfies a relationship of r1