To accurately control to keep a constant output light power of each wavelength channels if the number of wavelength channels convert in an optical amplifier which inputs multiple signal light wavelengths with fewer optical components.

This device is provided with a control circuit which inputs the optical output interruption information outputting from a plurality of light transmission parts, and always selects the optical output power setting voltage correspond to the number of wavelengths when the number of wavelengths to input to an optical amplifier changes, and moreover, adjusts the optical output power setting voltage per 1 wave by using the proportionality relation of the optical output power and the number of wavelengths.