This invention provides a storage system in which a volume containing WORM data is restorable. A control unit, after the copying is finished, consults a first meta data associated with data stored in a first block of the first volume, consults, in a case where the consulted first meta data including information indicating that the data stored in the first block of the first volume is prohibited from being updated for a given period, a meta data for a block that follows the first block of the first volume, and restores, in a case where the consulted first meta data does not includes information indicating that the data stored in the first block of the first volume is prohibited from being updated for a given period, data stored in the second volume into the first volume by copying data stored in a second block, which is associated with the first block of the volume, and is located in the second volume, to the first block of the first volume, thereby reproducing the data of the second volume in the first volume for restoration.