The controller of the image reading apparatus acquires second reference data indicating a reading value of a background plate by causing the reading unit to read the background plate during a non-document-reading period between a document-reading period and a document-reading period, calculates a first difference indicating a difference between a value in a first pixel range corresponding to an element group, among the plurality of photoelectric conversion elements, in a range under temperature influence by a given heat generation source and a value in a second pixel range, that is, part of a pixel range which does not fall under the first pixel range with respect to the second reference data, and updates, when the first difference exceeds a first allowable value, the first reference data by correcting a value in the first pixel range of the first reference data based on the first difference.