A storage system capable of cutting back the resource while obtaining a WORM function. A controller (110) functions to: obtain, when a write request is made by a computer (300), information on one of logical devices that is a target of a write process, from a memory module (140); and inform, when the logical device is set to unwritable, a signal indicating that the logical device is set to unwritable, to the computer (300). An interface (200) functions to: reference meta-information held in a disk drive (130) to obtain a list of files that are not accessed for a predetermined period; secure a logical device; and cause the controller (110) to store, the files on the list of files and set the logical device that stores the files in a manner that makes information stored in the memory module (140) unwritable.