The invention relates to backup processing for performing backup of data used in an information processing device having a storage unit. When data has been updated, updated bit information indicating that the data has been updated is stored in an update bitmap management table stored in the storage unit. When the number of updated bit information in the update bitmap management table has reached a differential backup reference value for estimating differential backup time, the backup of data corresponding to the updated information is commanded. When the command for the backup is received, the updated bit information stored in the update bitmap management table in the storage unit is read out. Then, the backup of the data corresponding to the updated bit information is obtained.