The present invention relates to a wavelength division multiplex optical transmission apparatus including an optical sending system having at least a plurality of optical sending sections to generate and transmit optical signals having different wavelengths [hereinafter referred to as optical signals] , a plurality of optical amplifying sections to amplify the optical signals, and a wavelength division multiplexing section to process by wavelength division multiplexing the optical signals after optical amplification. An optical output level control section is mounted in the apparatus to control, for the wavelengths, optical output levels of the optical signals output to the optical transmission line through the wavelength division multiplexing section by individually varying amplification factors of the optical amplifying sections in the optical sending system. It is thereby possible to adjust, for the wavelengths, send optical output levels of the optical signals having the plurality of different wavelengths, to be transmitted after the wavelength division multiplexing so as to transmit, for the wavelengths, the optical signals at optimal optical output levels.