FIELD: long-distance fiber-optic communication systems or multiplex systems. SUBSTANCE: amplifier has first measuring unit for metering power level of input optical signal; fiber-optic amplification unit for shaping pumping beam and amplifying input optical signal in compliance with desired check gain value; second measuring unit for metering spontaneous radiation power level in two preset short and long wavelength bands beyond wavelength region incorporating signal channel; and gain regulator designed to obtain output-signal gain characteristics according to measured power level of input optical signal and to control check gain value of amplification unit according to measured power level of spontaneous radiation to equalize amplification unit gain. EFFECT: enhanced degree of gain uniformity including when signal power level changes from one wavelength to other. 3 cl, 2 dwg
