1. An apparatus for supporting a document data search based on a keyword, comprising: an extraction unit for extracting a plurality of keywords from search target document data; a graph generation unit for generating a graph including a plurality of objects respectively representing the plurality of keywords extracted by the extraction unit and being classified into a plurality of clusters; and a search condition statement generation unit for generating a search condition statement by use of a keyword, in accordance with a user operation to select a specific cluster among the plurality of clusters in the graph generated by the graph generation unit, the keyword being represented by an object that belongs to the specific cluster.