A computer generates searching context information relating to appearance frequencies of words or semantic codes in a searching query sentence from the searching query sentence. Semantic analysis is performed on sentences included in documents so as to generate semantic structures, and each of the semantic structures includes three or more semantic codes and a relationship type among the semantic codes. A plurality of context information is generated and each context information relates to an appearance frequency of a word or a semantic code in a group of documents that match each of the semantic structures. The computer specifies one semantic structure of the semantic structures in accordance with the searching context information and the plurality of context information, and searches for a similar document by using the specified semantic structure.