PURPOSE: To distinctly display even a fine part of an original picture together with the original picture by displaying a partial picture on an independent window to simultaneously display the original picture and the partial picture.

CONSTITUTION: A partial display area of the picture is designated in a certain window (overall display window) 12 to display the picture of the partial display area on another window (partial display window) 13. A partial display control means 8 is provided which controls scrolling of the display part and the change of the display magnification and the display range in the partial display window 13. A part of picture data is taken out from the original picture and is displayed on another window (partial display window). Thus, parts (partial display areas) 121 and 122 on which parts of the original picture are displayed are moved to change display contents, and the position on the overall picture is easily discriminated.