Abstract: Entered symbols are converted by a code ID table to code IDs numbered in order of increasing code length. Code IDs outputted by the code ID table are replaced by means of an ID conversion table, after which the outputted codes are delivered to a code table and to a code-length table. A Huffman code outputted by the code table is packed by a packer based upon a Huffman code length outputted by a code-length table. In accordance with the local occurrence probability of entered codes, the ID conversion table 103 is updated per prescribed number of symbols. Accordingly, the correspondence between Huffman codes and symbols is altered dynamically and it is possible to prevent a decline in the efficiency of encoding of data in which there is a dynamic variation in the probability distribution (occurrence probability) of symbols.