A common external storage device is connected to the first and second storage systems. The management computer comprises a capacity expansion volume migration section that migrates a capacity-expansion volume that the first storage system comprises to the second storage system; a host connection path switching section that switches the host connection path being used from a first host connection path that links a migration source capacity-expansion volume and the host computer to a second host connection path that links a migration destination capacity-expansion volume and the host computer; and an external connection path switching section that switches the external connection path being used from a first external connection path that links a storage area allocated to the migration source capacity-expansion volume and the external storage device to a second external connection path that links a storage area that is allocated to the migration destination capacity-expansion volume and the external storage device.