PURPOSE: To simply attain a high speed process by outputting a code regarding an observation direction assigned by a density string encoding part, and outputting the variable density structure information of a remarked picture element from a variable density structure information output part setting the code string as an input.

CONSTITUTION: A multivalue density digital signal from a scanning and photoelectric transducing part 1, after it is stored temporarily at a multi-gradation picture storage part 2, is given to a density string output part 3. The density string output part 3 reads out the density signal of each picture element within a picture element area of 3×3 centering an optical remarked picture, and outputs picture element density strings regarding four observation directions. Density string encoding parts 4aW4d input the picture element density string classified at every observation direction obtained respectively from the density string output part 3, and output a density state after encoding. These four codes classified by every direction are given to a variable density structure information output part 5 and the density structure information of the remarked picture element is outputted.