PURPOSE: To allow high-speed processing by providing a run length counter circuit and a deformed Weyl coder which receives the output of this run length counter circuit and the one-dimensional binarized image signal string read out of an image signal FIFO as inputs and outputs a remainder code.

CONSTITUTION: An input image signal is inputted to the FIFO 41 in synchronization with an image signal input clock. The run length counter circuit 42 counts the continuous length of the white or black of the image signal and writes this length together with a color identification signal as run length information to the deformed Weyl coder 43. The deformed Weyl coder 43 accepts the run length information from the run length counter circuit 42 and the raw data (image signal) from the FIFO 41, encodes the same in accordance with a deformed Weyl code table and outputs the codes. Then, the max. code quantity to be generated per picture element is necessitated to be 1.33 bits and, therefore, the input speed of the image signal is increased. The prompt processing type one-dimensional coder of a high speed is obtd. in this way.