a read unit reads a plurality of pieces of image data from an image storing unit for output , respectively . a destination specifying unit specifies image display units to be display destinations of the image data from the read unit . a divided - period setting unit divides a unit display period of the image display units to a plurality of divided periods to correspond to the image display units . in each divided period , a synthesis unit synthesizes , for sequential outputs , the image data from the read units according to the display destination specified by the destination specifying unit in order to multiplex the image data to be displayed on each of the image display units . a separating unit separates , in every divided period of the unit display period , the synthesized image data for output to the image display units corresponding to the respective divided periods .