In a case where it is determined that image processing on image data is executed not in parallel with other image processing different from the image processing and printing of an image of the document is started after reading of an image of a first page of the document is completed, a transfer rate of image data from an image reading unit to an image processing unit is set to a predetermined transfer rate. Whereas in a case where it is determined that the image processing on image data is executed not in parallel with the other image processing different from the image processing and printing of the image of the document is started without waiting for the reading of the image of the first page of the document to be completed, the transfer rate is set to a transfer rate lower than the predetermined transfer rate.