Provided is an optical fiber having W-shaped refractive-index distribution and in which a micro-bend loss in an actual usage waveband is reduced. The optical fiber includes a core, inner cladding that surrounds the core and has a refractive index smaller than a refractive index of the core, and outer cladding that surrounds the inner cladding and has a refractive index smaller than the refractive index of the core and larger than the refractive index of the inner cladding. When a coupling coefficient between a fundamental mode and a cladding mode is denoted by C 01-CL , a coupling coefficient between the fundamental mode and a higher-order mode is denoted by C 01-11 , and a coupling coefficient between the higher-order mode and the cladding mode is denoted by C 11-CL , C total defined as C total = C 01-CL + C 01-11 C 11-CL has a minimum value at a wavelength ranging between 1520 nm and 1630 nm.