In the method, two originals are placed side-by-side on the contact glass of an electrophotographic duplex copying machine and are scanned successively, in a single scanning operation, by the exposure optical system of the machine to form respective successive images on a photoconductive drum rotated past an image transfer device. Two transfer sheets are fed successively, with a short interval therebetween, from a primary supply device for transfer sheets, past the image transfer device in synchronism with the image formation on the drum, to provide duplex copies, having images in the same relation as that of the two originals, in a single copying cycle or process. By utilizing a secondary sheet supply device and a suitable switching device, images can be provided on both sides or surfaces of a transfer sheet or sheets. The duplex copying apparatus includes a novel sheet feed device effective to stack transfer sheets neatly.