PURPOSE: To prevent a memory from being wasted and to surely perform garbage compaction processing even when plural cells refer to the same cell.

CONSTITUTION: When an area 1 is an object area of garbage compaction, the address D of a referring cell 4 is stored in an in-area reference cell control table 15 by using the address B of a cell 2 referred to by the cell 4 in the object area as a key, and the address E of a referring cell 5 is stored in an outside-area reference cell control table 16 by using the address of a cell 3 to be referred to by the cell outside the area as a key C; and the cells 1 and 4 which refer to the same cell 2 are linked to generate a list and after the referred cell 1 is rearranged, the addresses of the cells which refer to the cell 1 are taken out of the respective cell control table by using the address of the cell 1 as a key to rewrite the pointers of the linked calls.