Abstract: A swapping apparatus for use in a computer system for swapping data between a main storage and a secondary storage. The swapping apparatus operates with a reduced secondary storage capacity yet improves the overall performance of the computer system. The swapping apparatus is characterized in that whenever a process does not require the main storage, a control unit is notified of the non-requirement of the main storage in order to lower the priority of that process, collectively releasing a page-fixed region if the main storage space is insufficient. Also, an updating unit is notified so as to perform paging at a reduced use frequency of the page region. Whenever the main storage is again required, the control unit is notified of the requirement, thereby fixing the page-released region in order to raise the priority of use of the main storage by that particular process. The updating unit is then notified to perform paging at an increased use frequency.