A wavelength-division multiplexing transmitter that is capable of enhancing its ability to compensate for a difference in light intensity between wavelengths. The wavelength-division multiplexing transmitter includes an optical branching part for branching a wavelength-division multiplexed input optical signal into a plurality of optical signals, a plurality of wavelength-selective devices for selecting as output wavelengths the wavelengths of each of the optical signals branched by the optical branching part, and an optical coupling part for coupling the output wavelengths respectively output from the plurality of wavelength-selective devices. At least either the branching in the optical branching part or the coupling in the optical coupling part is performed at a power ratio M:N where M and N differ from each other.