1. A decoding device comprising: a buffer configured in memory to store N (N is a positive integer) code streams; and N decoders connected in series, each of the N decoders having a one-to-one correspondence with one of the N code streams, and being configured to decode the corresponding code stream and sequentially generate partial symbols of M bit width (M is a positive integer) per each unit cycle, wherein among the N decoders, i (2<=i<=N, i is a positive integer) stage decoders store multiple probabilistic models in the memory; and wherein, in each unit cycle, an i stage decoder receives an input of i−1 partial symbols which are partial symbols generated by an i−1 stage decoder in the former unit cycle, selects one probabilistic model among the multiple probabilistic models based on i−1 partial symbols which are entered previously, generates one partial symbol using previously selected probabilistic models, and outputs the previously generated one partial symbol along with the previously entered i−1 partial symbols.