1. An image-reading device comprising: a conveyor configured to convey one or more documents to a reading position; a reading unit configured to generate read data by reading, along a main-scanning direction at the reading position, the one or more documents that are being conveyed along a sub-scanning direction by the conveyor; and a control device configured to: detect candidate edge points in the read data, the detection being performed along a plurality of respective detection lines extending along the sub-scanning direction, the detection being performed from one end to the other end of each of the detection lines; determine a first edge based on locations of candidate edge points indicating an edge of the document; extract feature points from an area located on a one-end side with respect to the first edge in the read data; obtain a density of the extracted feature points, compare the obtained density and a threshold value, obtain a distance between a first document and a second document that are successively conveyed by the conveyor, and when the distance is smaller than a predetermined value, identify the first edge as a detection target edge based on the comparison result.