An image forming apparatus, including a reading device and a controller to control the reading device to execute a reading operation, is provided. The controller in the reading operation executes a leading edge detecting process, wherein a leading edge of an original sheet is detected from image data acquired through the reading device; a trailing edge detecting process, wherein a trailing edge of the original sheet is detected from the image data acquired through the reading device; a determining process, wherein one of the leading edge and the trailing edge to be used to correct the image data acquired through the reading device is determined based on conditions of the detected leading edge and the trailing edge; and a correcting process, wherein the image data is corrected by use of the determined one of the leading edge and the trailing edge determined in the determining process.