In an end surface closely arranged multicore optical fiber 200, at least two single-mode optical fibers 10 are, at one and the other ends of the individual single-mode optical fibers 10, closely arranged in parallel to each other and bound together, such that a center-center distance of adjacent single-mode optical fibers 10 is twice a core diameter of the single-mode optical fiber 10 or greater and 0.5 times a value obtained by subtracting the core diameter of the single-mode optical fiber from a core diameter of a multimode optical fiber to be connected or less, and that the remaining individual single-mode optical fibers 10 are individually independent from each other.