To provide a light diffusion plate suppressing degradation of brightness even with a reduced lamp image, and to provide an optical sheet, a backlight unit, and a display unit using the same.

The light diffusion plate is equipped with a transparent layer on an incident face side where incident light from a light source enters, and a diffusion layer on an emitting face side from which the incident light from the light source emits. In the region where a quantity of incident light from the light source to the incident face is large, a thickness ratio of the light diffusion layer to the light diffusion plate becomes larger. On the contrary, in the region where a quantity of light incident into the incident face from the light source is small, a thickness ratio of the transparent layer to the light diffusion plate becomes larger.

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