To reduce retrieval and analysis time for a specific code and referring to the specific code required for a signal processing unit promptly, by realizing high-speed retrieval replacing a sequential retrieval for all the encoded data group, in which the specific code is mixed at random.

The decoder includes a retrieval code table 131 for assigning the specific code to be retrieved, code-retrieving units 121, 122, 123 to 129 for retrieving the assigned specific code, and a code table forming unit 132 for recording information about the specific code retrieved by a code retrieving means. The encoding data group 110 is divided into retrieval regions of the same number as the code retrieving means. For each divided retrieval region, the specific code assigned by the retrieval code assigning means is retrieved.