Abstract: A code conversion system converts an MH code into an arithmetic code. In code conversion system, a template 93 which is necessary for an arithmetic decoding process is obtained in such a manner that MH code words corresponding to the template 93, which are derived from already MH coded reference lines 90 and 91 respectively, are decoded, and the decoded data are shifted in three shift registers A77, B72 or C80. By means of a signal indicative of completion of the arithmetic decoding process in an arithmetic decoding device 71 and a signal indicative of completion of a shift-in process in shift registers A77 and so on, the process of the arithmetic decoding device 71, a decoding process of an MH code word in an MH decoding device and an MH coding process in an MH coding device 74 can be executed simultaneously.