A plural number M (M≧2) of block cipher encryption units perform, in a block order, either encryption processing or decryption processing for data of a series of blocks each having a predetermined data size and included in a data unit. The plural number of block cipher encryption units perform either encryption of decryption for the data unit by repeating processing in the block order. Every time processing of a data unit starts, a block cipher encryption unit configured to process the data of the nMth (nM