Disclosed is an optical fiber, which includes: a core positioned at the center of an optical fiber to have the maximum refractive index within the optical fiber; an inner clad surrounding the core to have the minimum refractive index within the optical fiber; and an outer clad surrounding the inner clad to have a refractive index lower than that of the core and higher than that of the inner clad, wherein a difference Δncore-inner—clad between the refractive index of the core and the minimum refractive index of the inner clad is within the range of 0.00615 to 0.00645, and a difference Δnouter—clad-inner—clad between the refractive index of the outer clad and the minimum refractive index of the inner clad is 0.0006 or more.