A storage apparatus that provides a dynamically extensible virtual volume for a host apparatus that accesses the virtual volume is characterized by including: a management unit setting part for setting a management unit, with which an area for storing data sent from the host apparatus is divided on a predetermined-area basis for management, for a pool area that provides a storage area to be assigned to the virtual volume; and a management unit resetting part for resetting the management unit set by the management unit setting part via analysis of the status of access from the host apparatus to the data at a predetermined time to make the management unit optimum for the status of access from the host apparatus to the data.