An image reading apparatus capable of recognizing edge portions of an original image with precision is provided. The image reading apparatus uses an image reading unit to scan an original being conveyed and read an image of the original. The image reading apparatus includes an edge information obtaining unit and an edge determining unit. The edge information obtaining unit detects an image of an edge portion of the original image and obtains, for each point in a main scanning direction, edge information, which indicates whether or not an edge portion image is detected at the point in a sub-scanning direction. The edge determining unit conducts detection from at least one of two directions of the main scanning direction to detect a point where a given number of successive edge portion images are detected, and obtains an edge portion based on the detected point.