1. An apparatus for retrieving a structured document comprising: a processor that is programmed to retrieve the structured document, wherein the processor causes: a first specifying unit to specify a plurality of object documents from a plurality of structured documents being accessible via a network, the object document being the structured document according to retrieval condition, a first extracting unit to extract a text included in the object document, a second extracting unit to extract a metadata appended to the object document, the metadata being first data indicating the text of the object document and second data indicating a link relation between the object document and related documents, each of the related documents being the structured document associated with the object document, a second specifying unit to specify whether a description supporting the object document is included in the text of the each related document, an analyzing unit to analyze whether author information of a related document is included in a metadata appended to the related document based on the metadata appended to the object document, and a first calculating unit to calculate higher importance for the object document related to the related document having the author information thereof included in the metadata compared with important of the object document related to the related document not having the author information thereof included in the metadata; and further to calculate higher importance for the object document corresponding to the related document including the description supporting the object document compared with importance of the object document corresponding to the related document not including a description supporting the object document.