A storage system including a snapshot volume arranged to provide each of a plurality of snapshot generations to the host as a virtual volume and to store data having an identical content in one storage area, and in that a management unit is arranged to: determine, when the host sends a request to create the original volume as a new volume of a designated generation, whether the designated generation is a generation of the copy volume or not; overwrite data in the copy volume for a block address of the designated generation indicating the snapshot volume if the generation of the copy volume is different from the designated generation; and change mapping information of the copy volume to the mapping information of the original volume.