An image-reading apparatus and method for controlling the image-reading apparatus including a document plate where an original document is placed, a line image sensor that reads an image on the document plate by scanning to obtain image data, a reference-setting image that is placed outside a region of the document plate at a position where the line image sensor is able to read the reference-setting image, and a control unit configured to set a reference position when the image sensor reads the image, wherein the control unit detects the reference-setting image from the image data and, depending on a power-on state of the image-reading apparatus, selects the manner in which the reference position is set based on the reference-setting image.