PURPOSE: To reduce the changed variable and simultaneously to facilitate the control of files over several generations by producing only a control table to the changed data and executing DRAW together with the changed data.

CONSTITUTION: In a file writing state, a control table A relating to the corresponding file is written. Then a control table B which controls the changed data only is produced and written together with the changed data in a DRAW state. In a file reading state, the table A is read out on a main memory device and an initial file is read out with the table A. Then the tables B equivalent to the DRAWs of the necessary generations are selectively read out, and the changed files of the necessary generations are read out based on the tables B read selectively. The changed files are superscribed on the initial file for the production of the file of the corresponding generation. Thus the corrections are freely carried out with a small corrected variable. Furthermore a specific generation is designated and read out even in the case the corrections are given to several generations.