It is an object of the present invention to provide a display device in which images can be seen under a dark place to intense external light. In the display device, display is performed by changing the gray scale number depending on external light intensity, and display modes can be switched depending on contents displayed on the screen. An analog mode and a digital mode are switched depending on external light intensity. In an analog digital switching circuit, when a video signal is an analog value, a signal is outputted to a pixel array without any change and, when the video signal is a digital value, the signal is outputted to a circuit that performs a digital operation such as a latch circuit. Consequently, display gray scales of a pixel are changed appropriately. Accordingly, a clear image can be displayed. For example, it is possible to ensure visibility in a wide range of a dark place or under indoor florescent light to outdoor sun light.