An image display device is provided with an image memory for storing a first image as a target secret image; a synthesizing section for time-multiplexing the stored first image and a second image obtained by reversely converting the luminance of the first image; and an image display section for displaying the time-multiplexed image. An optical shutter which transmits light at the time of displaying the first image is arranged to the synthesizing section. The image display device is also provided with a display characteristic detecting section which fetches information regarding to the display characteristics of the image display section, and an image converting section which converts the first image into the second image, based on the fetched display characteristics of the image display section. Thus, the image display device effectively shields image display from a third party, even when the display characteristics of the the image display section are changed.