An optical path-changing device has a cladding having a first face, a second face, and at least one mirror surface; and cores, each core having a first core end surface exposed at the first face and a second core end surface exposed at the second face, each core providing a continuous optical path extending from the first core end surface to the mirror surface, changing in direction at the mirror surface, and extending to the second core end surface. The first core end surfaces and the second core end surfaces are arranged two-dimensionally at the first face and the second face, respectively. First pin insertion apertures on an exterior casing member accommodating the optical path-changing device provide positional adjustments relative to the optical axes of the first core end surfaces.