When a part already transmitted to an object storage is updated by a file system management section while a plurality of parts are being transmitted to the object storage, a file transfer section requests the object storage to generate a temporary object that is a temporarily generated object containing the transmitted and updated part by combining the parts transmitted before update, re-splits a file into a plurality of parts so that the transmitted and updated data and not-transmitted data are handled as parts different from transmitted and not-updated data, and transmits the part containing the transmitted and updated data or the part containing the not-transmitted data to the object storage.