PURPOSE: To binarily code only a target effectively by determining automatically a threshold in accordance with the histogram of a specific area of digital picture data and binary coding the specific area in accordance with the threshold and expanding the binary-coded picture to store it in a memory.

CONSTITUTION: A picture signal 2 picked up by an image pickup device 1 is converted by an A/D converting circuit 3 to become the first digital picture data 4A and is inputted to a frame memory 25 and a histogram operating circuit 26. The circuit 26 calculates histogram data 27 in accordance with data 4A and an expanded binary-coded picture 11D from a binary-coded picture memory 30 and supplies this data 27 to a threshold determining circuit 9. The circuit 9 receives data 27 to determine a threshold 10 and the threshold 10 is supplied to a comparing circuit 8 to obtain the first binary-coded picture data 11A from picture data 4B from the memory 25. A binary-coded picture expanding circuit 29 expands data 11B read out from a binary-coded picture memory 28 and stores expanded data in the memory 30.