A storage apparatus includes a data storage unit, management information storage unit, compression judgment unit, and compression control unit. The data storage unit stores the data of files. The management information storage unit stores management information on the files. The compression judgment unit evaluates compression effectiveness for a file at prescribed execution timing and determines whether the compression of the file is appropriate or not. The compression control unit updates the management information so as to reflect the determination result obtained by the compression judgment unit, and then stores the compressed data of the file in a compressed format in the data storage unit if the determination result indicates that the compression is appropriate, and stores the uncompressed data of the file in an uncompressed format in the data storage unit if the determination result indicates the compression is inappropriate.