An image scanning apparatus is capable of successively scanning a plurality of documents arranged on a document plate in an efficient manner by moving a sensor unit over the documents in a sub-scanning direction. When the plurality of documents arranged on the document plate is scanned, the motion of the sensor unit is selectively controlled in such a manner that after completion of scanning one document, the sensor unit is returned to its home position before starting scanning a next document, the sensor unit is temporarily stopped before starting scanning the next document, or the sensor unit is moved backward by a particular distance before starting scanning the next document.