Abstract: A display medium employing a diffraction grating to define and represent a display pattern by the contour thereof, which enables the display pattern to move smoothly as the visual point moves and which allows the display pattern to move in various ways and is easy to produce. A display pattern ("DNP"), e.g., a character, an image, etc., is defined and displayed by the outer or inner contour of a diffraction grating (A or B) composed of a group of smooth curves, or a diffraction grating composed of a group of partial straight-line diffraction gratings that form polygonal lines linearly approximating smooth curves. Accordingly, as the visual point is moved relative to the display medium, a position that looks bright by diffraction moves smoothly and variously. If the display medium is illuminated by white light, the region that looks bright becomes a rainbow-colored region. Accordingly, the display pattern becomes not only readily recognizable but also interesting to view.