PURPOSE: To restore and wake up information required for task restart from a detachable external storage device in spite of whether a system to wake up is a hibernation executed system or not.

CONSTITUTION: In the prescribed area of the external storage device, history information is stored for showing the hibernation is executed at the system to which the external storage device is mounted in the past. The wake-up system checks the history information and executes wake-up (step 1101). Besides, the external storage device stores control information containing system configuration information at the time point of task interruption. The wake-up system compares the stored system configuration information with its own configuration information (step 1102). When the configuration information is not coincident, the restore of information from the external storage device into a main memory is refused.