PURPOSE: To simplify separation of signal modes by separating signal modes by light wave length.

CONSTITUTION: When relay a is turned on, an intrinsic luminescence wave length range light beam generated by combination of luminous body A and optical band pass filter A1 is condensed by lens A2 and is incident onto light incoming end DA2 and is transferred to spectroscope D3 for fiber through spectroscope D2 for fiber and optical fiber D. Spectroscope D3 for fiber branches and sends lights which are incident onto light outgoing ends DA3, DB3 and DC3 equally. Lights from light outgoing ends are condensed by condenser lenses A3, B3 and C3 and are transferred to optical band pass filters A4, B4 and C4; however, optical band pass filters B4 and C4 cut off these lights, and only photo diode A5 is driven to generate an on signal from amplifier circuit A6. Similar operations are performed in case of turning-on of relays b and c, and further, simultaneous multiplex transmission is possible.