PURPOSE: To update rationally a data set, by setting master and slave relation relating to mutual directory and a rank of processing at data updating between a slave data set copied from a master data set being an original.

CONSTITUTION: The master data set 1 and the slave data set 2 copied from the master have directories 1a and 2a, and data 1b, 2b. The directories 1a, 2a are stored with information representing master slave relation and attribute. In inputting an instruction 5a to an update processing service section 5 of a processor 3, when the data A is copied to the data B, the address information to the slave data set and the update processing service level are recorded on the directory 1a. The service level updates the master and the slave data at the same time, updates the master data only and stores a notice sentence to the slave data, or updates the master data and sets on an alarm flag to the slave data depending on the frequency of usage of data and the importance. Thus, the revision work is rationallized.