PURPOSE: To attain multiplex transmission by providing plural light sources at one end face of an optical fiber and irradiating beams so that they may not align in parallel to each other.

CONSTITUTION: Drive circuits 4a∼5e drive corresponding semiconductor lasers 4a∼4e according to the signal fed from a signal source corresponding to each circuit. The laser light outputted from the laser 4a is made incident to one end face 6 at an incident angle θ1, then refracted at refraction angle θ2. Then the laser light is totally reflected on the interface between a core 2 and a cladding 3. The beams fed from each semiconductor laser have an equal incident angle to the face 6 and are not parallel to each other. Therefore, the light outputted from one end face 8 of the output side is outputted at the same angle as the angle θ1, however, these beams are not parallel to each other. Thus no crosstalk is produced.