PURPOSE: To demarcate a character string area and a document area even when a character string slants, by processing density information on the entire document picture with spatial two-dimensional Fourier transformation, and demarcating the character string area and document area on the basis of variation in the absolute value of a peak value.

CONSTITUTION: An input screen 1 is taken by an input camera 11 and a preprocessing part 12 performs density correction, digital filter processing, etc. Then, a two-dimensional Fourier transformation part 13 performs the two-dimensional Fourier transformation regarding the entire document picture to find the peak value close to an origin in the Fourier-transformed space, and a line-interval, position, and angle detection part 14 finds the line intervals of the whole. After the line intervals are found, a side decision part 15 finds small matrix size and a small matrix scanning part 16 searches the whole document with the small matrix size; and the result is processed by the Fourier transformation of a two- dimensional Fourier transformation part 17 to detect its peak point and a character and graph area demarcating part 18 demarcates the character and graph areas.