A diffuser sheet which compensates for chromatic dispersion generated in a hologram light guide plate, and an illumination apparatus employing the diffuser sheet are provided. The diffuser sheet includes a plate type light-transmissive substrate and a light diffusion layer disposed on a light emission surface of the light-emission substrate. A light-incident surface of the light-transmissive substrate has declined surfaces and flat surfaces which are alternatively and repeatedly formed thereon. The declined surfaces are declined at a predetermined angle.