In a dispersion slope compensator of the invention, angular dispersion of a WDM light in which the angular dispersion is already performed in a first direction (Y-axis) with a VIPA plate is performed in a second direction (X'-axis) perpendicular to the first direction with a diffraction grating, and the WDM light is reflected from a three-dimensional mirror and returned to the VIPA plate side. At this point, the three-dimensional mirror is mounted on a rotating stage while placed on a linear-moving stage, which moves the three-dimensional mirror in parallel in the second direction. Thereby, the rotating stage can adjust an angle of a reflection plane of the three-dimensional mirror with respect to an optical axis of the light focused with a lens, which allows optical axis shift of the reflected light to be corrected in the three-dimensional mirror according to setting of a chromatic dispersion compensation amount. Accordingly, chromatic dispersion compensation and dispersion slope compensation can be realized over a wide signal band.