1. A contents' relationship visualizing apparatus comprising: a usage history acquiring unit for acquiring usage histories of multiple contents; a users' set specifying unit for, by use of the contents' usage histories, specifying a content's users' set indicating users utilizing each content; a similarity calculating unit for, by use of a similarity index, calculating a similarity between the specified users' sets; and a network creating unit for, by use of the calculated similarity between the users' sets, creating a network indicating a relationship between the contents.