Abstract: There are provided a plurality of etalon filters arranged in concatenation, a light output portion for outputting a light to the etalon filters, and a light input portion to which a light transmitting the etalon filters is inputted, and the plurality of etalon filters have mutually different free spectrum regions. A plurality of etalon plates applied with semipermeable films to both surfaces of a thin glass plate and having mutually different periods and amplitudes are cascade-connected. By combining a plurality of etalon films having different characteristics with one another, it is possible to realize an optical equalizer having low loss polarized light dependency and capable of compensating optional gain wavelength dependency. By using such an optical equalizer as a repeater by combining the optical equalizer with an optical amplifier, a level difference caused by the difference of the gain among wavelengths of optical signals is neither produced in a wavelength multiple optical transmission apparatus.