A display device includes a main video data storage means for storing video data; a display mode storage means for storing a display mode; a display mode writing means by which a display mode of a supplied video signal is judged and the judged information is written to the display mode storage means; a video signal reading means by which the video data is read from the main video data storage means to supply to a display panel; a display mode reading means by which the display mode is read from the display mode storage means; and a video signal writing means by which permission or prohibition of writing of the supplied video signal is judged based on the display mode read from the display mode reading means and the video signal is converted to video data which can express a gray scale and written to the main video data storage means.
