To provide an optical modulator which relaxes the restriction on the transmission capacity of an up signal and down signal while effectively utilizing a wavelength resource and can suppress the occurrence of an SBS, in a wavelength multiplexing optical communication system with light sources concentrically arranged at a center node.

The optical modulator has a light intensity saturating means having input and output characteristics at which the output light intensity is saturated with respect to the input light intensity above the minimum saturated input intensity and a light intensity modulating means for outputting the input light after the intensity modulation thereof by a transmission signal. The modulator is constituted to input the signal light subjected to the intensity modulation in such a manner that the minimum value of the light intensity is above the minimum saturated input intensity to the light intensity saturating means, to input the output light thereof to the light intensity modulating means and to output the output as fresh signal light therefrom.