PURPOSE: To obtain an information transmitting network at a low cost by constituting it by a mixing element for dividing equally an optical signal which has been made incident from one optical fiber into a branch bundle sticking tightly to the other end face, by utilizing a total reflection of many times in the inside.

CONSTITUTION: A titled device is provided with a signal input/output terminal 10 whose constituting elements are a few optical fibers of a minute diameter and one large aperture optical fiber, a fiber 11 used for light emitting element for leading an output of a light emitting element to a mixing fiber 13, and a fiber 12 used for photodetector for leading an optical output which has transmitted through a mixing fiber 13, to a photodetector. When a signal is made incident to the mixing fiber 13 from one of the light fibers 11 for light emitting element serving as one element of the signal input/output terminal 10, a total reflection in the inside becomes asymmetrical with respect to the axis since the mixing fiber 13 is bent, therefore, said signal becomes uniform on the end face of a signal output/input terminal 14 side of the mixing fiber 13, and divided equally to plural terminal use fibers 15 having an equal diameter, which are stuck tightly to its face.