An image-reading device may include a reading unit and a control device. The control device may be configured to detect a candidate point for an edge of the document on each of a pair of parallel detection lines, obtain a tilt angle of a straight line extending between the detected candidate points in the read data and classify the obtained tilt angle into a plurality of range groups. Further, control device may be configured to count the number of obtained tilt angles in each of the plurality of range groups. Also, each of the range groups may be associated with a predetermined angle and when the count of one of the range groups meets predetermined criteria, the control device may assign the predetermined angle of the range group whose count meets the predetermined criteria to be a tilt angle of the document.