The dispersion compensator with an etalon and a mirror arranged in parallel or at a slight angle with respect to each other is constructed so that emitted light from a collimator is reflected by the etalon multiple times and then enters another collimator. The dispersion compensator also has dispersion compensating units that change temperature using a heater or equivalent in order to render the amount of dispersion variable. In addition, these dispersion compensating units are provided in multi-stage form, and the angle of the mirror, the amplitude reflectance of the etalon, and temperature are optimized to offer polygonal dispersion characteristics. This realizes a practical, variable dispersion compensator suitable for a wavelength division multiplex optical transmission system and capable of shifting a variable amount of dispersion to the plus or minus side.