Display light projection optical device

A display light projection optical device, having characteristics in which display light emitted from a display unit is reflected in a vicinity of one surface and is projected to a predetermined eye point, and in which external light incident on an other surface is transmitted in a thickness direction, the display light projection optical device comprising:

• a first optical member that is transparent and is formed in a thin plate shape;
• a Fresnel-shaped portion that is formed by a plurality of grooves which are concentric with each other on one surface of the first optical member in a thickness direction thereof;
• a half mirror layer that is formed on a surface of a Fresnel-shaped portion;
• a second optical member that is formed of a transparent filler for filling unevenness of a surface of the half mirror layer to form a flat surface;
• and
• a third optical member that has a transparent thin plate shape and protects an outside surface of the second optical member,
• a refractive index of the first optical member, a refractive index of the second optical member, and a refractive index of the third optical member are substantially equal.