A digital image reading apparatus is provided, which apparatus includes a reading part for optically reading an image of a document to output digital image data, a first setting part for setting a reading rate in a given scanning direction to a desired value, an image memory for temporarily storing the image data, a second setting part for setting parameters related to reading the image of the document based on communication with an external apparatus, and a computation part for computing a total amount of the image data from the parameters, wherein the first setting part sets the reading rate based on the total amount of the image data.