PURPOSE: To prevent duplicated write on a decoded line and also to attain high speed processing by using the constitution where a change point address of the present decoded line is loaded to the address counter of a line memory for read of the next reference line.

CONSTITUTION: A microprogram ROM27 is a memory storing a sequence of microinstruction and the microinstruction read from the microprogram ROM27 is written in the next pipeline register 28 and executed at the leading of the next clock by the control of the sequencer 26. The sequencer 26 supervises each signal of decoding line change point detection, reference line change point detection, reference line end, coded line end and decoded transmission response through a selector 24 at all times when the sequencer does not execute the operating processing, and when the sequencer 26 finds out the signal, the processor outputs the address of head address of the microprogram ROM27 to which the sequence to the signal is stored during one clock and transfers the control for the execution of sequence.