An object of the present invention is to provide a storage controller capable of facilitating extension of storage capacity while suppressing investment related to storage capacity.The present invention has achieved the storing of system configuration information including content of a definition, set externally, of a virtual volume with storage capacity that is larger than a real storage capacity composed of the storage capacity of a storage device unit, and content of a definition, set externally, of at least one of a real volume formed as a result of dividing the real storage capacity, and a pool area; and communicating the storage capacity of the virtual volume based on the stored system configuration information in response to a storage capacity confirmation request from the host system, and, based on the system configuration information, writing or reading relevant data to or from a relevant address position in the storage device unit in response to a data input/output request from the host system designating an address in the real volume, and writing or reading relevant data to or from the pool area in response to a data input/output request from the host system designating an address in the virtual volume other than the real volume.