An image forming apparatus including an automatic document feeder (ADF) that transports a document is provided. The ADF unit includes a subtray that is openable and closable. When transporting a document, the subtray is opened and a document to be transported is fed into a space below a guide member. At this time, surfaces of the subtray and a main tray are used as a feed tray. The document that has been transported is discharged onto a guide member and is further transported onto the surface of the second tray. At this time, the surface of the second tray and the surface of the guide member are used as a discharge tray.