1. A document image processing apparatus, comprising: a display portion for displaying a document image; a line input portion for inputting a line portion manually input along the image of an arbitrary character string in the document image displayed at said display portion; and a processing portion for processing the line portion manually input by said line input portion, said processing portion including, direction determining means for determining the direction of the manually input line portion, row extracting means for extracting the region of a row including the image of said arbitrary character string in the region of said document image based on the direction determined by said direction determining means and at least one character image in said document image, and line correcting means for correcting said manually input line portion into a normal line portion drawn along the region of said row extracted by said row extracting means, thereby displaying the normal line portion at said display portion.