1. A ruled line extraction apparatus, comprising: a first binarization device generating a first binary image by binarizing a multiple-valued image; a second binarization device generating a second binary image by binarizing the multiple-valued image in a method different from a method of said first binarization device; an extraction device extracting a ruled line candidate area using the first binary image; a determination device determining whether the extracted ruled line candidate area corresponds to a ruled line using the second binary image; and an output device outputting information about a ruled line candidate area determined to correspond to a ruled line.