PURPOSE: To improve the transaction processing efficiency by reserving a requirement and the prescribed record showing an allocated page as a transaction log in the case of requiring an allocated page to be an idle state and setting the state display that is decided by the end state of a transaction and its log.

CONSTITUTION: A data control part 22 receives a processing requirement from a transaction 26 and refers to an area control table to select a page in the case of requiring the page in an idle state to be allocated. When a requirement is received for the security of an idle state of the allocated page, the page designated by the requirement is selected. Then the state display corresponding to the page selected via the area control table is defined as a second state display. Thus the requirement and the prescribed record showing the selected page are reserved as a log of the transaction 26. When the transaction 26 is ended, the state display decided by the end state and its log of the transaction 26 is set as the state display corresponding to the relevant page of the area control table. Thus the transaction processing efficiency is improved.