PURPOSE: To utilize the memory area effectively and to give flexibility to the system by dividing the memory area variably and controlling the memory area.

CONSTITUTION: Prior to the expansion of data from a data file 1 to a data expansion area 3, data for the expansion is expanded at the head of the head segment 31 of the data expansion area 3 to generate a master pointer table 310 and data having a data identifier entered into a master pointer table 310 are expanded into segments in order while the segment size of a segment control table 2 is updated. Then, the pointers of data by data identifiers are recorded in the master table 310. Consequently, the data area on the memory can be utilized effectively and the system is given the flexibility.