When a file server is to create data that does not permit falsification in an external storage, it is not possible to guarantee that the rewriting of this data can be prevented from a computer connected to the external storage without going through a file server. Provided is a storage system configured from a first storage having a file I/O processing unit and a second storage connected to this first storage, wherein the first storage includes a unit for requesting a change of access authority to the storage area in the own storage and in the second storage provided to the own storage. An access request to a storage area in a second storage from a computer connected to a second storage without going through a file I/O processing unit is restricted based on the change of access authority executed by the second storage upon receiving the request from the first storage.