Problem: Providing a storage system which can be applied to a broad range of access forms to the file and, at the same time, in which the performance of file access control processing is improved. Solution: The storage system stores a part of the access control information of a variable size in the basic attribute area of the file, and stores the storage format information in the basic attribute area of the file or in the file system metadata area. At the time of processing the access to the file, with reference to the storage format information, the storage system decodes a part of the access control information into an access mask bit string as needed, and performs the preceding access control processing. If whether access is permitted or not can be determined through the preceding access control processing, the access control processing is performed while, whether access is permitted or not cannot be determined, performs the access control processing based on the extended attribute information.FigureFIG. 7