PURPOSE: To decrease the time from the reservation accept from the user till the notice representing the acceptance of the reservation by reading reservation acceptance management information managed in time series for each resource use start date and time from a master memory device directly, releasing the write protection and setting it.

CONSTITUTION: A protection area 21 in which no write write is possible at the normal program operation and write is possible only at the write by a reservation system is provided to a main storage device 2 connecting to a central processing unit 1. When the reservation of resource is received by a user request party, the write protection is released, a data is written and the write protection is set again. The data is written in the write protection area 21 of the main storage device 2 at the reservation acceptance and the data is written afterward to an external storage device 3 in the lump. at the fixed time cycle. Number of times of write to the external storage device is reduced more than a conventional method writing data to the external storage device for each acceptance of reservation.