PURPOSE: To change the number of digits in data managed by a system while corresponding to the operating form of a user.

CONSTITUTION: A before-change data form management part 6 checks whether data are present in a before-change data form management file 12 or not by a data retrieval part 7 and when data are present thereon, the validity of change contents is checked according to the data. When there is no problem, a data changing part 5 changes the data in a data form management file 11 and when no data is present in the before-change data form managing file 12, the validity of change contents is checked according to the data in the data form managing file 11. When there is no problem, the data in the data form managing file 11 are changed, and a data registration part 8 registers the data on the before- change data form managing file 12 as the data before the change.