The liquid crystal display device performs display by changing the number of gray scales depending on external light intensity, and switches the display mode in accordance with a content to be displayed on a display. By controlling a display mode-specific video signal generation circuit depending on external light intensity, an inputted video signal is outputted as an analog value, is outputted with a digital value of a binary, or is outputted with a multiple digital value. As a result, display gradation of a pixel changes timely. Accordingly, a clear image can be displayed. For example, a display device which secures visibility can be obtained in a wide range from under fluorescent light in a dark place or indoor to under outdoor sunlight.