The size of management information pages for storing format management information is minimized and a management size of the management information pages is reduced.A storage system has a controller(s) for managing an area of a management-information logical unit, which stores format management information to manage whether an access-target logical unit has been formatted or not, by using a former page area and a latter page area, wherein when formatting the access-target logical unit, the controller: calculates a capacity of the format management information based on a capacity of the access-target logical unit; calculates the number of management information pages according to a ratio of the calculated capacity of the format management information to a page management unit; allocates the format management information of one page to the former page area and manages its storage location by using a former page area address; and allocates the format management information of two or more pages to the latter page areas and manages their storage locations by using latter page area addresses and a page length.