401 are optical transmission lines such as optical fibers reference numerals 411 419 are terminals for performing communication reference numerals 421 429 are active optical nodes for conducting light transmission light receiving and communication control and reference numeral 480 is a repeater optical amplifier for amplifying the optical signal in fig1 which shows as an example the structure of one of the active optical nodes 422 the reference numerals 450 and 451 are opto electric converters o e for converting the optical signal to an electric signal reference numerals 440 and 441 are electro optical converters e o for converting the electric signal to the optical signal and reference numerals 430 is a communication controller the controller 430 discriminates if the signal transmitted through the transmission lines 400 and 401 and converted to the electric signal is addressed to the terminal 412 and if so the controller 430 transmits the signal to the terminal 412 and if not so the controller 430 again converts the signal to the optical signal using the e o devices 440 and 441 to transmit this signal to the optical transmission lines 400 and 401 further when the signal is transmitted to the controller 430 from the terminal 412 the controller 430 converts the signal to the optical signal using the e o devices 440 and 441 and transmits it to the transmission lines 400 and 401 under such control that the signal will not collide with the optical signals from the other terminals the reference numerals 491 494 are optical amplifiers which comprise of optical semiconductor devices of this invention the operation of this embodiment will be explained taking the case in which the signal.