A display device for use in compact portable devices is configured for assigning gray levels according to the pixel area ratio and, further includes a digital-to-analog (D-A) conversion circuit for converting digital data to gray-level voltage or analog signals. This configuration reduces the size of the circuit for D-A conversion, thus reducing the space for the driving circuit when assigning gray levels according to the pixel area ratio. The combination of the gray-level voltage output from the driving circuit and the gray-level assignment according to the pixel area ratio reduces the scale of the circuit.