Abstract: A reflection mirror of a projection display unit which displays a stereoscopic image through a light polarization glasses, reflects a linearly polarized light emitted from a projection source through a polarizing plate toward a screen. The reflection mirror includes: a glass substrate; a metal film provided on the glass substrate; a first dielectric film provided on the metal film; and a second dielectric film provided on the first dielectric film, wherein each of the first and second dielectric films includes a predetermined thickness and a predetermined refractive index so that a phase difference between a p-polarized light of a reflected light and a s-polarized light of the reflected light is within a range from -45 degree to 45 degree in case of an incident angle of the linearly polarized light being varied from 0 degree to 45 degree.