A Raman gain control method of controlling a Raman gain caused by simultaneous
application of pump lights of a plurality of wavelengths to an optical fiber, which
includes, based on a relation of a ratio coefficient which is a ratio of power
of each pump light to total power of all the pump lights with the Raman gain, from
a designated value of the Raman gain, calculating power of each pump light realizing
the designated Raman gain within a designated wavelength range, and controlling
power of each pump light applied to the optical fiber to apply each pump light
at each power calculated.
