An image forming apparatus includes a plurality of memory devices, each including at least one image memory which stores image data. A controller controls input and output operations for the image data relative to the at least one image memory. An image reading device generates image data by scanning and reading an original document. At least one data input device inputs image data generated by an external source. A plurality of input paths transmit the image data generated by the image reading device and the image data input by the at least one data input device. An image memory switching device connects the plurality of input paths to the plurality of memory devices, receives the image data generated by the image reading device and the image data input by the at least one data input device, and switches the plurality of memory devices to transmit consecutive image data, which is consecutively sent through one of the plurality of input paths, to a same memory device among the plurality of memory devices when the image memory switching device receives the image data and the image data through the plurality of input paths.