Optical transmission apparatus and optical attenuation amount control method

An optical attenuation amount control method by an optical transmission apparatus for controlling an attenuation amount, at the time of performing first channel transmission using a first number of channels, so as to transmit an amplified spontaneous emission light along a no-signal channel, of a wavelength which is within a determined range from a wavelength of a signal light channel, the method comprising:

• determining by a processor that switching from a second channel transmission using a larger number of channels than the first number of channels to the first channel transmission has been performed;
• and referring, according to the determining, to a storage device which stores information regarding a channel from which an optical transmission apparatus at a subsequent stage drops a signal light, and making, in the case of the no-signal channel the wavelength which is within the determined range from the wavelength of the signal light channel used in the first channel transmission being the channel which the optical transmission apparatus at the subsequent stage drops a signal light, an attenuation amount in the no-signal channel larger than a determined value.