PURPOSE: To reduce transmitting time, by performing MH encoding in processes which require high speed encodings and converting the MH codes into MR codes at the time of transmission.

CONSTITUTION: When MH codes which can be encoded at high speed are input, an MH encode line extracting circuit 1 extracts the head line of the MH codes and gives a detecting signal to an EOl "1" insert circuit 2. In this way, the insert circuit 2 adds "1" to the head line and sents it to a code output buffer 3. At the same time, the MH code is sent to an MR code circuit 6 through a K-line buffer memory 5 and encoded into MR codes, after it is decoded at a MH decode circuit 4. Upon receiving the MR code, the buffer circuit 3 outputs converted MR codes. Since MH codes encoded at high speed in this way are transmitted after they are converted into MR codes, the transmitting time is reduced.