An optical-fiber light amplifier using rare-earth-doped optical fibers. The light amplifier combines first and second excitation light from first and second sources to form combined excitation light and divides the combined excitation light for inverted distribution to both two optical fibers. The light entered one optical fiber and that entered the other optical fiber are polarized so as to be perpendicular to each other so that fluctuation of output level is prevented without mutual interference. Alternatively the first excitation light and the second excitation light may have different wavelengths; also in this case, fluctuation of level is prevented without any interference.
