PURPOSE: To perform the reorganization without stopping a data base system by executing partially the reorganization with respect to a data file, and repeating it until the processing is ended with regard to all store units in the data file.

CONSTITUTION: A reorganizing means 2 starts a partial reorganizing means 3 successively with respect to a store unit in a data file 1, and the partial reorganizing means 3 starts a store unit read-in means 4 with respect to two or more store units and reads in data records in the store units in a lump onto a memory 5, and subsequently, starts a store unit generating means 6, reorganizes the store unit in accordance with a prescribed rule from the data records which are read in onto the memory 5 and reorganizes partially the data file 1. The reorganizing means 2 repeats these partial reorganizations, and when the store unit which does not conform with the rule is generated, the partial reorganizing means 3 is started with respect to its store unit and other store unit, and the processing is continued until the processing is ended with regard to all the store units in the data file 1.