3. The computer-readable medium according to claim 2 , wherein the extracting is adapted to select a graphic that makes the element parameter to be found within the corresponding parameter range from the document image and consolidate a plurality of ruled line elements that make the consolidation parameter to be found within the corresponding parameter range to generate the ruled line candidate.
3. The computer-readable medium according to claim 2 , wherein the extracting is adapted to select a graphic that makes the element parameter to be found within the corresponding parameter range from the document image and consolidate a plurality of ruled line elements that make the consolidation parameter to be found within the corresponding parameter range to generate the ruled line candidate. 6. The computer-readable medium according to claim 3 , wherein the ruled line is a solid ruled line; and the extracting is adapted to divide the document image expressed by a binary system into a plurality of regions, select regions that make the element parameter to be found within the parameter range out of the regions as ruled line elements and consolidate the ruled line elements to generate a ruled line candidate.