A two-sided copying method and apparatus for a digital copier having an automatic document feeder (ADF) and a two-sided tray device. Documents sequentially fed by the ADF are read by a CCD image sensor and stored in a memory in the form of digital image data. The image data representative of odd pages of the documents are sequentially read out of the memory the highest-numbered page or the lowest-numbered page being first, the image data being printed out on one side of individual paper sheets. The resulting one-sided copies being temporarily stacked on a two-sided tray device. Then, the image data representative of even pages of the documents are sequentially read out of the memory with the lowest-numbered page or the highest-numbered page being first. The one-sided copies are refed one by one from the two-sided tray device the uppermost copy or the lowermost copy first, so that the image data associated with the even pages are reproduced on the other side of the individual one-sided copies. The resulting two-sided copies are driven out of the copier to a tray in the correct order of the pages.