1. An image processing apparatus comprising: an optical character recognition section that generates a document image by optically reading a paper document, executes optical character recognition on the document image, and outputs a character recognition result; an item name extraction section that obtains a character string semantically corresponding to an item name of an extraction target by natural language analysis and extracts, from the character recognition result, a first character string as a character string relevant to the item name of the extraction target; an extraction item storage section that stores extraction item information containing an item name of an information item and a relative position of an item value corresponding to the item name within a document image; an item value extraction section, operatively connected to said item name extraction section and said extraction item storage section, that retrieves information of a relative position of a second character string from said extraction item storage section, the relative position of the second character string being a location in the document image in the vicinity of the extracted first character string corresponding to the item name in one or more of left, right, upper, lower, lower left, lower right, upper left, and upper right directions from the extracted first character string, and extracts the second character string of an item value corresponding to the item name based upon the retrieved relative position of the second character string, the second character string being different from the first character string; and an extraction information creation section that creates extraction information by associating the second character string of the item value extracted by the item value extraction section to the item name.