An examining device adapted to examining a transmittance of a display panel is provided. The examining device includes a light source, a first polarizer, a photodetector, a second polarizer, at least one first reflector and at least one second reflector. The light source and the photodetector are respectively disposed on both sides of the display panel. The second polarizer is disposed between the display panel and the photodetector. The first reflector is disposed between the display panel and the second polarizer. The second reflector is disposed between the display panel and the first polarizer. Light emitting from the light source successively passes via the first polarizer, the display panel, the first reflector, the display panel, the second reflector, the display panel, the second polarizer and then emits into the photodetector.