Conventional dispersion compensators were not sufficient to satisfy a demand to set a different dispersion value for each WDM wavelength in a ring-mesh type network that utilizes wavelength selective switches or the like. The devices were insufficiently reduced in size and power consumption and used with difficulty to change dispersion characteristics for each wavelength flexibly in a simple manner. A dispersion compensator of the present invention uses general-purpose optical components including a spatial light modulator for providing discrete phases to set appropriately the relationship between the focusing beam radius and the spatial light modulator pixel, thereby providing various dispersion compensation characteristics. Attention is focused on the correspondence between multiple pixels on the spatial light modulator providing discrete phases and a communication channel band, thereby allowing for changing the flexible dispersion characteristics and realizing the setting of an independent dispersion value for each WDM wavelength.