A wavelength division multiplexing optical transmission apparatus includes a plurality of polarization multiplexing optical modulation means, polarization-maintaining optical multiplexing means, and delay adjustment means. The polarization multiplexing optical modulation means generate a plurality of polarization multiplexed optical modulation signals having different wavelengths. The polarization-maintaining optical multiplexing means multiplexes the wavelengths of the polarization multiplexed optical modulation signals to generate a wavelength multiplexed optical signal (WDM). The delay adjustment means adjusts a delay such that light intensities of polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal (WDM) vary inversely with respect to each other.