Abstract: Disclosed is an illuminating display device for use with a mosaic panel, in which necessary display devices, measuring instruments, and the like are mounted to a crosswise-shaped metallic grid, to form a panel surface, and on which light-emitting diodes are arranged at a high density to afford a high-luminance display surface. The illuminating display device prevents the display surface and the interior of the display device from increasing in temperature to high due to heat generated by a large number of light-emitting diodes. The whole illuminating display device is composed of a base frame (4) mountable to and removable from the grid, and a circuit board (5) and a reflector (6) to be mounted on the base frame.