An optical bus system comprising an optical bus is furnished, along two opposed edges, with a plurality of signal light input/output portions for inputting and outputting signal light to and from the bus. Any one of the signal light input/output portions on one edge of the bus inputs signal light thereto and propagates the light to the opposite edge at which another signal light input/output portion outputs the propagated signal light from the bus. The system also comprises a plurality of light emitting/receiving circuits corresponding to the signal light input/output portions. Each light emitting/receiving circuit has a signal light sending unit and a signal light receiving unit. The signal light sending unit generates signal light and sends the generated signal light into the optical bus through the corresponding signal light input/output portion. The signal light receiving unit acquires a received light signal upon receipt of the signal light output by the corresponding signal light input/output portion. At least one of the light receiving/emitting circuits on each edge of the optical bus has a repeating or reflecting part that causes the corresponding signal light sending unit to send out the signal light received by the corresponding signal light receiving unit.