PURPOSE: To shorten the task holding time by enabling a task to access save information in the middle of check point save processing.

CONSTITUTION: A memory release means 17 checks a check point processing indicating means 11-2 of a management information block whose release is requested, when the check point processing is not executed, the release processing of the management information block is executed, and when the check point processing is executed at present, one is subtracted from the value in a reference counter 11-1 of the management information block, and it is checked whether a check point write means 14 is the release request source or not, and the processing is terminated when it is not the release request source. When it is the release request source, indication of the check point processing in the check point processing indicating means 11-2 is erased, and the processing is terminated if the value of the reference counter 11-1 of the management information block is not 0, but otherwise, the release processing of the management information block is executed. Thus, the task holding time is shortened.