An integrated database system comprises a plurality of database systems connected to one another through a network, each of the plurality of database systems managing its own stored data independently of the other database systems and accessing the stored data in accordance with an access request, and an integrated database unit connected to the network. The integrated database unit includes a directory database which stores a correspondence between each of the data stored in the plurality of database systems and a database system in which each of the data is stored, a directory control unit which acquires, by using the directory database, directory information corresponding to target data of the accepted access request, a database identifying unit which identifies a database system, and a database control unit which issues, on the basis of the acquired directory information, an access request to the database system having the target data of the accepted access request. The database system includes a database server unit which accesses a database in accordance with the access request issued by the integrated database unit.