PURPOSE: To reduce an overhead at the time of an update processing at low cost.

CONSTITUTION: Usable directories 15 for distributively storing the same data item in duplicate into plural base processors 2, 3 and 4 are stored in directory storage devices 11 which are mutually connected via communication lines and which store and manage information on the constitution and arrangement of the data item. A simultaneous execution control management device 12 executes simultaneous execution control for controlling plural simultaneous retrieval update processings on duplicate arrangement information on the distributed and duplicate data item by the usable directory 15. In such a case, a retrieval update processing means 13 substitutes update to the distributed and duplicate data item with update to directory information. A data restoration means 14 copies the latest data item at the time of actual retrieval and update.