1. An image reading apparatus comprising: a reading device configured to read a document image; and a control unit, wherein the control unit configured to perform: an image reading process of controlling the reading device to read the document image every line and acquire read data of respective lines; a line ground-color-density detection process of detecting a ground-color-density of respective lines from the read data acquired by the image reading process; a line count process of counting the number of adjacent lines, which is the number of lines that are adjacent to each other and a difference of the ground-color-densities of the lines falls within a reference range, based on a detection result of the line ground-color-density detection process; a document ground-color-density extraction process of extracting a ground-color-density of a line in an area having the largest number of adjacent lines from a read image of the document image, as a ground-color-density of the document image, based on a count result of the line count process; and a density determination process of determining whether the ground-color-density of the document image extracted in the document ground-color-density extraction process is a reference density or lower, and a ground color correction process of performing, when it is determined in the density determination process that the ground-color-density of the document image is the reference density or low, a ground color correction for the read data, in response to the ground-color-density of the document image.