The invention provides a data management device which is well suited to grasp featuring parts from among a huge amount of data, which are capable of enhancing the reliability of extraction and which can immediately comply with a user's request. In particular, feature data for calculating the temporal transition of similarities concerning the contents of document data can be extracted from the document data of a document data registration database, the change point of the similarities can be specified on the basis of the extracted feature data, and document data are retrieved from within the document data registration database on the basis of the specified change point. In the retrieval, the document data which belong to the specified change point or the vicinity thereof can be retrieved.