PURPOSE: To improve the encoding rate of an encoding section or the like, by discriminating the storage state of picture signals at the transfer to a line memory or from the line memory for displaying the state at a header section.

CONSTITUTION: The line memory 2 consists of a picture signal storage section and the header section. In storing the picture signal in the line memory in this constitution, the presence of a line black picture element is detected in parallel and it is displayed on the header section. Since the presence of the black picture element is displayed on the header section without an excessive processing time as to the line stored in the line memory in this way, an encoder recognizes the line without the encoded information by referencing the header section, allowing to eliminate the need for the run lengt count. Thus, the encoding efficiency of the encoder is improved and the stability of the subscanning control system is improved.