A backup method is provided for a file system for managing hierarchical storage including one or more storage media on a computer system including one or more computers. Each of the one or more storage media includes a data part which is separated from an index and on which updated information is appended and kept. Each of a plurality of pieces of data within the file system is managed to be migrated to at least any of the one or more storage media. The backup method includes backing up metadata of the plurality of pieces of data migrated within the file system; and backing up the index of each of the one or more storage media to which the plurality of pieces of data have been migrated, substantially at the same time point as the metadata.