A storage system including a primary storage device having a primary volume, and a secondary storage device having a secondary volume, a generation restoration portion, and a generation management volume. The secondary volume receives differential information from the primary volume to remote copy information in the primary volume and the differential information is stored in the generation management volume and grouped by generation. The generation restoration portion restores a storage content of a specified generation and grouping is conducted by a condition set in the secondary storage device, wherein the condition could be changed by a user.