A chromatic dispersion compensator includes an optical circulator or a directional coupler having a first, second and third ports; an input transmission path connected to the first port; an output transmission path connected to the third port; a chirped grating connected to the second port; and a dispersion compensating fiber connected to at least one of the first, second and third ports. The dispersion compensating fiber and the chirped grating have chromatic dispersion characteristics which are opposite to the chromatic dispersion characteristics of the input and output transmission paths. In the wavelength compensator, the optical signal is incident into the first port from the input transmission path, and is made to go out to the chirped grating from the second port. Further, the optical signal is incident from the chirped grating to return to the second port, and is made to go to the output transmission path from the third port.