An image reading apparatus which includes an image reading section and a document conveyance section, the image reading apparatus including: a document size detector which detects a document size of the document; and a processor configured to detect whether or not a Z-fold exists in the document for which the document size is detected by the document size detector; unfold a Z-folded part of a Z-folded document for which a Z-fold is detected; and assign image data of the image to a page memory on the basis of the document size detected by the document size detector and whether or not a Z-fold is detected.