PURPOSE: To execute binary picture encoding with a high compression ratio by selecting a processing whose encoding efficiency is high at the time of MH encoding with picture data which is convolution-processed before the encoding pre-processing of binary picture data and picture data which is not convolution- processed in every main s can direction line.

CONSTITUTION: A first convolution processing means 6-1 which executes the convolution processing of binary picture data is provided. A first exclusive OR processing means 13-1 which takes the exclusive OR of picture data of n-bits at every picture element, and first and second change point detection means 7-1 and 7-2 detecting the change point of picture data which is convolution-processed and picture data which is not convolution-processed are provided. A change point number comparison means 8 compares the number of the change points which the detection means 7-1 and 7-2 detect. A selection processing means 10 selects the processing of a side where the data compression rate becomes high at the time of encoding by using picture data which is convolution-processed and picture data which is not convolution-processed.