The object of this invention is to provide an image processing apparatus in which, in processing of a document image read by a document reading device, an inclination of a character string in the document image which is recognized in character recognition is obtained more accurately. The image processing apparatus includes a similar character extraction portion which extracts and outputs a character group comprised of characters having a shape and a size that are same with or similar to each other from among characters constituting a character string comprised of a character recognized in optical character recognition from a document image read by a document reading device; and an inclination calculation portion which calculates an inclination value of the character string based on position information of each character of the character group output from the similar character extraction portion.