1. An information retrieval method including: a step in which a processing unit receives, through an input unit, input for a retrieval query Q including information related to nodes, labels of nodes and links among the nodes; a step in which the processing unit finds a set F of solution candidates as a result of searching the database in response to the retrieval query Q by making reference to a thesaurus storage unit storing thesaurus T for defining a degree of similarity among the labels of nodes, using similarity among the labels defined by a subset R of thesaurus T according to links that are input, and making reference to a database D storing the nodes and labels that are input; a step in which the processing unit displays a set F of solution candidates that are found on a display unit; a step in which the processing unit receives, through the input unit, input information related to whether some elements in the set F of solution candidates are representing the solutions; a step in which the processing unit deletes some elements in the set F of solution candidates from the set F of solution candidates according to input information; a step in which the processing unit deletes, adds or changes the contents of the subset R and/or the retrieval query Q based on input information related to deleting, adding or changing the subset R of the thesaurus T and/or the retrieval query Q input through the input unit; and a step of returning to the step of retrieval if there is a request for re-retrieval from the user to repeat the processing, or ending the processing if there is no request.