1. A data processing device generating a graph which expresses an input data structure by a plurality of nodes having a single word as content thereof and by a dependency branch connecting two nodes in a dependent relationship within the plurality of nodes, and extracting a characteristic structure characterizing the input data from the graph, the device comprising: an association node extraction unit for extracting nodes semantically associated with each other, which are nodes corresponding to words representing same or similar content, from each of sentence structures in a given sentence structure collection, and outputting information on the sentence collection and association nodes in each of the sentence structures; an association node joint unit for joining the nodes semantically associated with each other in each of the sentence structures by a semantic association branch based on the information on the sentence structure collection to newly generate a structure that expresses a concept which is not present, but implied, in each original sentence structure, and the association nodes in each of the sentence structures received from the association node extraction unit so as to transform each of the sentence structures in the sentence structure collection, and outputting a structure collection obtained by the transformation; and a characteristic structure extraction unit for extracting a characteristic partial structure based on the sentence structure collection transformed by joining the semantic association branch received from the association node joint unit, wherein the characteristic structure extraction unit performs characteristic structure extraction processing by distinguishing a branch indicating a dependent relationship in the graph structure from the semantic association branch.