To confirm contents of an annotation without calling out an annotative input window even while reading a document displayed on a screen.

An annotation input part 102 reads in respective annotative data constituting the annotation stuck to a specified annotative position on the document from a document file 100 by being inputted through the annotative input window to gain the information of the input positions and sizes of these annotative data. An annotative image magnification revision part 105 generates the reduction or expansion image of the display image of the annotation based on the information of the input positions and sizes of respective annotative data in the annotation gained by the annotation input part 102, and a magnification shown by a magnification hold part 104. A document/annotative image simultaneous display part 109 generates the display image superimposing the reduction or expansion display image of this annotation on an annotative position specified by a user on a document display image 107 to display it on a document display screen 111 of a display device 110.