The present invention transfers replication logical volumes between and among storage control units in a storage system comprising storage control units. To transfer replication logical volumes from a storage control unit to a storage control unit, a virtualization device sets a path to the storage control unit. The storage control unit prepares a differential bitmap in order to receive access requests. When the preparation completes, the virtualization device makes access requests to the storage control unit. The storage control unit hands over the access requests to the storage control unit. The storage control unit performs a process so that the access requests are reflected in a disk device and performs an emergency destage of storing data in a cache memory into disk device. When the emergency destage ends, the storage control unit connects to an external storage control unit and hands over access requests to the external storage control unit.