An encoder includes an information holding section which stores flag bytes and an initial address, a data generation section which generates sets of first parity symbols from the initial address and the flag bytes, a parity generation section which generates and outputs sets of second parity symbols, for each column of data units included in the block, from the columns of data units included in the block and input user control data. The data generation section generates the addresses and the sets of first parity symbols, required to generate the columns of data units included in the block, based on the initial address and the flag bytes, selects necessary portions from the flag bytes and the addresses and the sets of first parity symbols generated, and outputs the portions to the parity generation section, as the columns of data units included in the block.