A transmitter of a communication system includes a spectrum dividing section which divides a transmission signal into a plurality of sub-spectra at a first sampling speed F1 and combines one or more low-speed intermediate composite signals from the divided sub-spectra, and a multiplexing section which multiplexes the intermediate composite signals at a second sampling speed F2 faster than the first sampling speed F1 (F2>F1) and distributes to a broadband. A receiver includes a demultiplexing section which extracts one or more low-speed intermediate composite signals from a reception signal at the second sampling speed F2, and a spectrum combining section which combines the intermediate composite signals at the first sampling speed F1 and extracts the sub-spectra to re-combines the transmission signal.