A coupled multi-core fiber 10 includes a plurality of cores 11 and a clad 12 surrounding the plurality of cores 11, wherein the plurality of cores 11 are arranged in such a way that periphery surfaces of the adjacent cores 11 contact with each other, each of the cores 11 is made to have a refractive index higher than the clad 12 and includes: an outer region 16 having a predetermined thickness from the periphery surface; and an inner region 15 made to have a higher refractive index than the outer region 16 and surrounded by the outer region 16.