In a multicore fiber in which multiple single mode cores are stored in one optical fiber, the multicore fiber has a lattice-point arrangement in which multiple lattice points are periodically arranged two-dimensionally with translational symmetry and rotational symmetry or one of translational symmetry and rotational symmetry and, in that lattice-point arrangement, multiple cores are arranged with the lattice points of the lattice-point arrangement as reference positions. By giving different perturbations to the propagation constants of the cores, the propagation constants of the cores are each varied from the original propagation constants. Because of the variation in the propagation constants, the core-to-core coupling amount, which is dependent on the varied propagation constants, fall below a predetermined setting amount. Suppressing the coupling between homogeneous cores in this way reduces the distance between the homogeneous cores, thus increasing the core density of the multicore fiber without increasing the types of heterogeneous cores.