A light diffuser and its use are provided, which not only reduces a color change in a source light when the light diffuser is disposed on an optical path of a light source, but also has a good light transmission property and a good light diffusion property. The light diffuser contains a thermoplastic resin and transparent particles added thereto. The total light transmittance of the light diffuser is 75% or more. The degree of dispersion of the light diffuser is 2° or more, the degree of dispersion being defined as a transmission angle at which a light transmittance is 50% of a rectilinear light transmittance when light is emitted to a surface of the light diffuser in a direction normal to the surface. The difference between the rectilinear light transmittance at 460 nm and the rectilinear light transmittance at 580 nm of the light diffuser is 0.96% or less.