PURPOSE: To ensure the processing operations of a compiler through a small working area even in case the size of a data group is larger than the size of an actual working area, by providing a page allocation control part, a segment output part which outputs segments to an external memory when the number of pages exceeds a fixed level, and a segment input part.

CONSTITUTION: A page allocation control part 110 starts a segment output part 130 when the number of allocate pages of a segment 220 exceeds the prescribed threshold value. The part 130 outputs all pages 210 forming the segment 220 existing within a working area 200 to a block 310 of an external memory 300. When a segment changeover request is produced, a segment switching part 120 works to start the part 130 for output of the current segment 220 to the memory 300. Then a segment input part 140 is started for input of a saved segment 320 of the memory 300 to the area 200.