A light source apparatus configured to supply light in a specific polarization direction to an image display apparatus includes a point or surface light source, an optical unit configured to reduce a divergence angle of light from the light source, and a light guide body having a reflection surface configured to reflect the light from the light source and propagate it to the image display apparatus, the reflection surface of the light guide body is arranged so as to face the image display apparatus, and a reflection type polarization plate and a retardation plate are arranged in order from a side closer to the image display apparatus between the image display apparatus and the reflection surface.