An image reading apparatus includes: a partial pre-scanning device configured to convey a reading unit in an edge detection area and causes the reading unit to execute a reading operation in the edge detection area, the edge detection area being a partial area within a scannable area on a platen, and a detecting device configured to detect a plurality of edge pixels on a basis of image data, the plurality of edge pixels representing a side of a document, the image data being outputted by the reading unit that reads the edge detection area through execution of the reading operation by the partial pre-scanning device. Upon the plurality of edge pixels not detected on the basis of the image data, the partial pre-scanning device moves the edge detection area in a conveying direction of the reading unit and causes the reading unit to execute the reading operation.