To reduce the effect of external light and to improve the accuracy of detecting the location of a touch. In an image-capture period, light emission from a self-light-emitting element is controlled, and imaging data at the time of displaying white on a display screen and imaging data at the time of displaying black on the display screen are output from each sensor pixel. The location of a sensor pixel where a difference between the two pieces of imaging data output from the same sensor pixel is the greatest is detected. Thus, the location of a touch of the object on the display screen is detected with high accuracy. By utilizing a difference between imaging data at the time of reverse display, the effect of external light can be reduced.