Position detecting device

A position detecting device comprising:

• a rear projector that projects an image;
• a projection screen that displays the image projected from said rear projector;
• imaging means that, from a rear side of said projection screen, takes an image of light emitted from a pointer that points from a front side of said projection screen including the entire image projected on said projection screen by the projector;
• and
• coordinate calculating means that analyzes the image taken by said imaging means to detect a two-dimensional position in a detection area where the light from said pointer is detected,
• further comprising a warpage preventing member that prevents warpage of said projection screen, and a treatment for preventing light reflection is applied to a plane of incidence of said warpage preventing member where light from said rear projector is incident.