A display apparatus is adapted to display a plurality of graph structures by aggregating the plurality of graph structures into a single graph structure, where each of the graph structures is made up of a plurality of elements. An acquisition hardware unit acquires graph structures at a plurality of time points in a time series. A distinguishing hardware unit distinguishes unchanged elements and changed elements in the graph structures. An aggregating hardware aggregates the graph structures. A display hardware unit displays the aggregated graph structure such that the unchanged elements and the changed elements are identifiable. A contracting hardware unit contracts two or more unchanged elements and, in response to displaying the aggregated graph structure, displays a single contracted element instead of the two or more unchanged elements.