To display a graph using a syntax tree as a display object without impairing readability.

An input means 1 inputs input information including syntax trees. A digest extracting means 2 creates a digest in regard to each syntax tree. A graph display means 4 extracts each syntax tree and displays a graph. In such a case, the graph display means 4 displays the graph including the digest in a position which should display the syntax tree. When a user indicates selection of any one of the digests, a selection ascertaining means 7 specifies a syntax tree corresponding to a digest in a cursor position on the basis of cursor position information inputted from a cursor moving means 6. The selection ascertaining means 7 sends specification information of the syntax tree to a syntax tree display means 5 along with syntax tree display form information inputted from a syntax tree display form selecting means 8. The syntax tree display means 5 displays the syntax tree in accordance with a display form indicated in the syntax tree display form information.