PURPOSE: To transmit plural pieces of information regardless of transmission distance without deteriorating transmission quality, by transmitting light, which has wavelength selected according to the transmission distance, through one optical fiber by a wavelength-multiplex transmission system.

CONSTITUTION: From cameras 61∼64 at different distances to monitors 11∼14 installed in a monitoring room etc., pictures are transmitted via one optical fiber cable consisting of optical fibers 71∼74. When the cameras 61∼64 send picture signals to optical transmitters 51∼54, the transmitters 51∼54 generate carriers with wavelengths λ1∼λ4 assigned according to transmission distance, and then are modulated by the picture signals and applied to optical synthesizers 41∼44, which receive them to transmit light waves of respective wavelengths each through optical fibers 71∼74, respectively. Then, the transmitted optical picture signals are separated by an optical branching filter 3 into original waves by the wavelengths, which are supplied to optical receivers 21∼24 to be converted into electric signals, which are supplied to the monitors 11∼14.