To provide a backup system and a backup method which can efficiently compress or back up data in accordance with the kind of the data.

The backup system includes a plurality of data formats, and backs up and stores data to be backed up, said data being composed of blocks of optional length. The backup system is provided with; a compression category storage part 36 which stores a plurality of compression categories; compression hardware 32 which compresses the data to be backed up for each block in accordance with a plurality of compression categories stored in the compression category storage part 36; and a storage means which stores a plurality of the data thus compressed. The backup system compares the data amount of a plurality of the compressed data and that of the prior-to-compression data, selects the compressed data of minimum data quantity or non-compressed data of minimum quantity, and backs up and stores the compressed data of minimum data quantity or non-compressed data of minimum quantity.