An image forming method for use in image forming apparatus including on the right surface thereof a discharge opening connectable with a post-processing device, the image forming method comprising the steps of:a first step of delivering one or more documents to a read position sequentially starting from the first document to read the documents at the read position, and outputting the documents in the form of images of the same posture as document images to be read on the documents;a second step of reading a document at a position where the same is placed and outputting the document in the form of an image of the same posture of a document image to be read on the document;a third step of forming, on the upper surface of a sheet to be supplied from the left surface side of the image forming apparatus, the images output in the first or second step in the order that they are read, and delivering the formed images in a direction of the right surface of the image forming apparatus; anda fourth step of reversing the sheet in such a manner that the upper surface of the sheet on which the images are formed in the third step is turned over to the lower surface of the sheet, and discharging the reversed sheet to the discharge opening.