An object of the invention is to provide a wavelength division multiplexing optical transmission apparatus and a wavelength division multiplexing optical transmission method which are capable of reducing the transmission quality deterioration of polarization multiplexed optical signals generated in an optical fiber transmission line and are suitable for dense wavelength division multiplexing. A wavelength division multiplexing optical transmission apparatus (11) includes a plurality of polarization multiplexing optical modulation means (2-1 to 2-N), polarization-maintaining optical multiplexing means (3), and delay adjustment means (4). The polarization multiplexing optical modulation means (2-1 to 2-N) generate a plurality of polarization multiplexed optical modulation signals (P-1 to P-N) having different wavelengths. The polarization-maintaining optical multiplexing means (3) multiplexes the wavelengths of the polarization multiplexed optical modulation signals (P-1 to P-N) to generate a wavelength multipl
