An optical transmission apparatus comprising: a branching unit configured to branch a wavelength-multiplexed optical signal (S IN ) including an optical signal of a first wavelength into a first branched light (S1) and a second branched light (S2); a first wavelength selection unit configured to block an optical signal of a first wavelength band including the first wavelength in the first branched light (S 1); a filter unit configured to allow passage of an optical signal (SD1) of a second wavelength band including the first wavelength in the second branched light (S2); and a multiplexing unit configured to receive an optical signal (SA1) of a second wavelength, to multiplex an optical signal (ST) output from the filter unit and the optical signal (SA1) of the second wavelength, and to output the multiplexed optical signal (S OUT ), wherein the second wavelength band is wider than the first wavelength band, the second wavelength band is a wavelength band that includes the first wavelength band, a first wavelength margin provided on a short wavelength side of the first wavelength band, and a second wavelength margin provided on a long wavelength side of the first wavelength band, the first wavelength band is a wavelength band that includes a wavelength band of the optical signal (SD1) output from the first wavelength selection unit , a third wavelength margin provided on a short wavelength side of the wavelength band of the optical signal (SD1) output from the first wavelength selection unit , and a fourth wavelength margin provided on a long wavelength side of the wavelength band of the optical signal (SD1) output from the first wavelength selection unit , the first wavelength margin is wider than the third wavelength margin, and the third wavelength margin is wider than the fourth wavelength margin. a branching unit configured to branch a wavelength-multiplexed optical signal (S IN ) including an optical signal of a first wavelength into a first branched light (S1) and a second branched light (S2); a first wavelength selection unit configured to block an optical signal of a first wavelength band including the first wavelength in the first branched light (S 1); a filter unit configured to allow passage of an optical signal (SD1) of a second wavelength band including the first wavelength in the second branched light (S2); and a multiplexing unit configured to receive an optical signal (SA1) of a second wavelength, to multiplex an optical signal (ST) output from the filter unit and the optical signal (SA1) of the second wavelength, and to output the multiplexed optical signal (S OUT ), wherein the second wavelength band is wider than the first wavelength band, the second wavelength band is a wavelength band that includes the first wavelength band, a first wavelength margin provided on a short wavelength side of the first wavelength band, and a second wavelength margin provided on a long wavelength side of the first wavelength band, the first wavelength band is a wavelength band that includes a wavelength band of the optical signal (SD1) output from the first wavelength selection unit , a third wavelength margin provided on a short wavelength side of the wavelength band of the optical signal (SD1) output from the first wavelength selection unit , and a fourth wavelength margin provided on a long wavelength side of the wavelength band of the optical signal (SD1) output from the first wavelength selection unit , the first wavelength margin is wider than the third wavelength margin, and the third wavelength margin is wider than the fourth wavelength margin. <EOS>