PURPOSE: To easily realize a special effect without imposing a load on the MPU or the like of a system, in the display system of a picture or the like.

CONSTITUTION: This device is equipped with a fine voltage generating means 10 which finely changes and outputs a prescribed constant voltage in an arbitrary cycle, and a superimposing means 12 which superimposes the output of the fine voltage generating means 10 on the reference voltage Vref of a D/A converter. Thus, an analog signal being the output of the D/A converter can be finely changed by superimposing the output of the minute voltage generating means 10 on the reference voltage Vref of the D/A converter.