PURPOSE: To detect a necessary schematic picture at high speed by dividing an area from a hue, lightness and a coordinate value after the picture is once reduced and synthesizing and re-dividing a divided result.

CONSTITUTION: A signal conversion means 3 receives the reduced picture and extracts information on the hue and lightness. An area division means 4 divides the area into several ones from information on the hue, lightness and the coordinate. An area synthesis/re-division means 5 synthesizes and re-divides the area. An isolated point in the clustered area is assumed that it is not included in any area and the size of the edge of a part which is brought into contact with the other area is obtained from the reduced picture and is calculated. When the size of the edge is smaller than a specified value, the area is considered to be continued and the areas are synthesized. The areas are synthesized as to the part which is not brought into contact with the other area when differences in lightness and the hue in the area are smaller than a threshold and when the peak of the histogram in the hue of the corresponding picture and a second peak are within the prescribed range in the area. A schematic picture generation means 6 gives a color representing a synthesis/re-division area.