A multicore fiber includes: n pieces of first core regions in a circular shape with a radius r1 that are arranged about points P11 to P1n, and that has a first core portion and a first cladding portion; a second core region in a circular shape with a radius R1 that is arranged about the point a1, and that has a second core portion and a second cladding portion; and a cladding region that is formed on an outer circumferences of the first core region and the second core region. Further, abutting surfaces that are flat surfaces abutting on each other are formed in portions on the outer circumferences of the first core region and the second core region.