The invention relates to a storage device in which MR-IOV is applied to the internal network of a storage controller, whereby the size of the storage device can be easily expanded. The storage device is expanded on the basis of a network having processor-connected RPs, FE I/F, BE I/F, and CM I/F that are connected with a switch. In the switch, a plurality of ports other than those connected to the RPs, FE I/F, BE I/F, and CM I/F are connected with a cross-link. Each processor is allowed to control the FE I/F, BE I/F, or CM I/F either via a path that passes through the cross-link or via a path that does not pass through the cross-link within the unit device. When unit devices are connected to expand the size of a storage device, the cross-link is removed first and then the unit devices are connected with a new cross-link (see FIG. 4).