PURPOSE: To make distribution and mixing of light bidirectionally among four pieces of optical fibers possible by using four pieces of reflecting mirrors of a columnar shape of a rectangular equilateral triangle.

CONSTITUTION: The light transmitted in an optical fiber 12 disperses at a π/2 cut cylindrical type focusing lens 16, and emits from its optical output face as parallel rays. Roughly one third of the parallel rays is reflected by a reflecting mirror 20, and is made incident to a π/2 cut cylindrical focusing lens 15, and the remaining one third is reflected by a reflecting mirror 21 and is made incident to a π/2 cut cylindrical focusing lens 17. Roughly one third the remaining parallel rays goes through the space created between the mirrors 20 and 21 and the mirrors 19, and 22 and is made incident to a π/2 cut cylindrical focusing lens 18. Hence, the light propagating in the fiber 12 is uniformly distributed to optical fibers 11, 13, 14. The same holds true of the light propagating in the fiber 11, 13 or 14.