To provide a light source unit for a luminaire using a general white LED as a light source, which adjusts color tone in addition to an excellent color rendering property, and excels in uniform light irradiation.

A diffusion sheet and a reflective sheet respectively containing dyes or phosphors of specific colors different from each other, and a light guide are combined with one another; light emitted from a white light source LED is made to permeate the diffusion sheet through the light guide; light in the light guide bottom direction is also made to permeate the diffusion sheet by being reflected to the upper surface of the light guide plate by the reflective sheet; color tone adjustment is adjusted by the dye or phosphor in permeating the diffusion sheet; by the diffusing action of the diffusion sheet, light without having been converted in wavelength by the phosphor, and light converted in wavelength by the phosphor are mixed in color by the diffusing action of the diffusion sheet to provide uniform light reduced in irregular color.