An optical transmission apparatus comprising: receiving interfaces configured to receive data output from an external terminal as electrical signals, signal light generators configured to convert the electrical signals received from the receiving interfaces into polarization multiplexed signal lights, a wavelength division multiplexer, and an optical amplifier configured to amplify a wavelength multiplexed light to be transmitted; characterized by: a non-signal light combining unit comprising a polarization maintaining coupler (132, 135), a polarization rotation element (133, 136) and a polarization beam combiner (134, 137), the polarization maintaining coupler (132, 135) having the function of branching off polarized non-signal lights, the polarization rotation element (133, 136) having the function of rotating the branched off non-signal lights in such a way that angles formed between polarization planes of the plurality of non-signal lights of a wavelength of wavelengths belonging to an amplification band of the optical amplifier become equal, and the polarization beam combiner (134, 137) having the function of combining said non-signal lights having an equal angle formed between the polarization planes, the wavelength being different from a wavelength of the polarization multiplexed signal lights being outputted from the signal light generator received by a wavelength multiplexer, whereby the polarization multiplexed signal light contains two signal lights of the same wavelength, the two signal lights whose polarization planes are orthogonal to each other; wherein the wavelength multiplexer is configured to generate the wavelength multiplexed light to be input to the optical amplifier by multiplexing a plurality of non-signal lights combined by the non-signal light combining unit and the polarization multiplexed signal light. receiving interfaces configured to receive data output from an external terminal as electrical signals, signal light generators configured to convert the electrical signals received from the receiving interfaces into polarization multiplexed signal lights, a wavelength division multiplexer, and an optical amplifier configured to amplify a wavelength multiplexed light to be transmitted; characterized by: a non-signal light combining unit comprising a polarization maintaining coupler (132, 135), a polarization rotation element (133, 136) and a polarization beam combiner (134, 137), the polarization maintaining coupler (132, 135) having the function of branching off polarized non-signal lights, the polarization rotation element (133, 136) having the function of rotating the branched off non-signal lights in such a way that angles formed between polarization planes of the plurality of non-signal lights of a wavelength of wavelengths belonging to an amplification band of the optical amplifier become equal, and the polarization beam combiner (134, 137) having the function of combining said non-signal lights having an equal angle formed between the polarization planes, the wavelength being different from a wavelength of the polarization multiplexed signal lights being outputted from the signal light generator received by a wavelength multiplexer, whereby the polarization multiplexed signal light contains two signal lights of the same wavelength, the two signal lights whose polarization planes are orthogonal to each other; wherein the wavelength multiplexer is configured to generate the wavelength multiplexed light to be input to the optical amplifier by multiplexing a plurality of non-signal lights combined by the non-signal light combining unit and the polarization multiplexed signal light. a non-signal light combining unit comprising a polarization maintaining coupler (132, 135), a polarization rotation element (133, 136) and a polarization beam combiner (134, 137), the polarization maintaining coupler (132, 135) having the function of branching off polarized non-signal lights, the polarization rotation element (133, 136) having the function of rotating the branched off non-signal lights in such a way that angles formed between polarization planes of the plurality of non-signal lights of a wavelength of wavelengths belonging to an amplification band of the optical amplifier become equal, and the polarization beam combiner (134, 137) having the function of combining said non-signal lights having an equal angle formed between the polarization planes, the wavelength being different from a wavelength of the polarization multiplexed signal lights being outputted from the signal light generator received by a wavelength multiplexer, whereby the polarization multiplexed signal light contains two signal lights of the same wavelength, the two signal lights whose polarization planes are orthogonal to each other; wherein the wavelength multiplexer is configured to generate the wavelength multiplexed light to be input to the optical amplifier by multiplexing a plurality of non-signal lights combined by the non-signal light combining unit and the polarization multiplexed signal light.