US Patent 7567354 Image copying device

A copy machine completes the reading in of the front surfaces of a plurality of documents, before starting reading in of the rear surfaces of the documents, and starts forming images before the reading in of the rear surfaces of all the documents has been completed. After the front surfaces of all the plurality of documents have been read in, the reading of the rear surfaces starts. It takes a period of time from a time T2 to a time T7 to read in image data of a quantity (Q2−Q1) from the rear surface of one document as apparent from a line segment 200a that is indicative of the speed at which the read-in image data is stored. The timing of printing start is offset to ensure that the line segment 200a and the line segment 300b do not intersect with each other. This makes it possible to start printing based on image data for the rear surface of the document while the reading of the subject surface of the subject document. It is possible to prevent the image data from running out regardless of the difference between the storing speed and the read-out speed.