The present invention is aimed at providing a low-cost optical transmission system of simple configuration, capable of achieving a satisfactory OSNR even in the time of transmission of a small number of wavelengths. To this end, the optical transmission system is provided with a noise elimination unit corresponding to each of optical amplifiers arranged on a transmission path. This noise elimination unit includes a transmission characteristic capable of selectively transmitting a light in a wavelength band in which a signal light exists through an amplification band of the optical amplifier, and includes a function of automatically eliminating a noise light in a wavelength band in which a signal light does not exist, of noise lights generated in the optical amplifiers.