PURPOSE: To provide the space rearranging system to preparing an empty area when there is no allocation enable area in the case of reallocation processing.

CONSTITUTION: This system is composed of a high-speed filing managing means 1, input/output control means 1, magnetic disk device control means 7 to control a magnetic disk device 8, free area managing table 3 to manage the area on the magnetic disk device 8, logical/physical mapping managing table 4, reallocation processing means 6 to operate the tables 3 and 4, transfer processing means 5 to transfer data, and rearrangement processing means 9 to rearrange data and to prepare a valid space. Then, the efficiency of spacing on the magnetic disk device can be more improved by rearranging the data.