A data server which partially constitutes a data management system in cooperation with another data server connected via a network, the data server having: a data management section that stores a data item; a user authentication section that performs user authentication; a searching section that searches the data management section for a requested data item when a data request is received from a client; a data providing section that provides the requested data item to the client when the requested data item is found in the data management section; and a redirect section that, when the requested data item is not found in the data management section, detects a data server which stores the requested data item in the data management system, receives temporary authentication information from the data server, and sends information to identify the requested data item in the data server and the temporary authentication information to the client.