The present invention is so arranged as to include (a) gradation reference potential generating means including a group of output terminals whose voltages are determined in accordance with a voltage division ratio of one ladder resistor, so as to output gradation reference potentials, for example, of 1024, which is a 16 multiple of a required 64-gradations; (b) output terminal designating means including a memory for designating, among from the output terminals, an output terminal for each of the 64-gradations required, in accordance with the display modes; and (c) selecting means for selecting an output terminal that corresponds to an input gradation signal, among from the output terminals designated by the output terminal designating section, and for applying a voltage via the thus selected output terminal to a display screen. With this arrangement, it is possible to attain very similar gradient signal-brightness characteristics for respective display modes with high accuracy, in order to prevent a gradient display from being changed due to switchover of the display modes.