Abstract: A reading unit of an image reading apparatus has a configuration in which a plurality of line sensors, including a first line sensor and a second line sensor that are arranged apart, are regularly arranged. The relation 0.95?L/(n×D)?1.05 (n=integer from 1 to 5) is satisfied where L is a distance between the first line sensor and the second line sensor in a sub scan direction. Before reading a document, the image reading apparatus detects an edge of the document, from which an image is to be actually read, using the first line sensor and the second line sensor to acquire correction information about document reading.