To discriminate short ruled lines, which cannot be extracted with a fixed threshold or dynamically estimated threshold, with a high precision.

In this ruled line discrimination method, runs whose run attribute information are not lines are used to extract a linked rectangle (15), and a short ruled line is decided based on lengths of runs included in a linked rectangle unit (16). If a ruled line is brought into contact with the upper or lower end of the short ruled line at right angles, this short ruled line is decided as a column line (17), and if the column line is used as a ruled line for frame extraction, the column line is extended and is registered as a ruled line. Extracted ruled lines are used to extract a frame (18), and character rectangles are extracted from the frame (19).