In a system where a first storage system and a second storage system are connected to a third storage system, when the first storage system virtualizes and provides a device in the third storage system as a device in its own storage system, update data stored in a cache in the first storage system is written into the device of the third storage system to be reflected, attributes of the device are transferred to the second storage system, and the second storage system virtualizes the device of the third storage system as a device of its own storage system.