Document reading apparatus that reads document images of documents by image sensors

An image forming apparatus that reads a document image of a document by a line sensor, in which image sensors are arranged in a main scanning direction, while moving the document and a carriage, to which a light source that irradiates light on the document through a contact glass is attached, relative to each other in a sub-scanning direction, the document reading apparatus comprising:

• a reading-position-detection plate arranged inside of a reading width of the line sensor and outside of a document-image-reading width, and having a color region, the length of which gradually decreases or gradually increases in the main scanning direction as going away from a home position of the carriage;
• a reading-position-detecting unit that detects the length in the main scanning direction of the color region on the basis of an output from the line sensor;
• a movement-distance-converting unit that converts the length in the main scanning direction of the color region to a movement distance to the home position;
• and
• a movement-control unit that causes the carriage to move toward the home position by the movement distance.