In a communication system using a sheet-shaped light guide (91), which includes particles for scattering light in a sheet-shaped optical medium and propagates signal light incident from one end face of the sheet-shaped light guide to the other end face side while scattering the signal light by the particles, when the sheet-shaped light guide (91) is connected with optical fibers (21 to 24, and 31 to 34) the diameters of which are larger than the thickness of the light guide, the optical fibers (21 to 24, and 31 to 34) and the sheet-shaped light guide (91) are joined with tapered light guides (92) interposed therebetween, the tapered light guide becoming thinner from the optical fiber side thereof to the sheet-shaped light side thereof.