1. A document requesting system for requesting a document providing system to transfer related documents, said document requesting system comprising: an extracting unit configured to extract from a first document transferred by request an identifier specifying a second document linked with the first document; a determining unit configured to determine a depth of link between the second document specified by said extracted identifier and a predetermined document as a reference, the second document being determined to be one of the related documents in a case where the depth of link is smaller than a specific value; and a requesting unit configured to request said document providing system to transfer the second document in the case where the depth of link is smaller than the specific value, wherein said determining unit includes a number-of-levels counter which counts a number of levels that indicates what level of hierarchy the second document falls from the predetermined document as the reference.