An active matrix display device having pixels disposed in a matrix is provided. Each pixel is divided into sub-pixels with different areas. The display device includes an inputting portion, multi-bit memories, digital-to-analog conversion circuits, display elements, and a conversion portion. The inputting portion inputs image digital data from outside of the active matrix display device. The multi-bit memories are disposed respectively for the sub-pixels and store input digital data with at least two bits, which serves as gray level information for gray-scale displaying of the sub-pixels. The digital-to-analog conversion circuits convert the input digital data to analog data which is used for the gray-scale displaying. The display elements perform the gray-scale displaying according to the analog data. The conversion portion converts the image digital data to the input digital data according to a predetermined gamma value waiting to be achieved and an area ratio of the sub-pixels.