Document transport apparatus and document transport method, and image reading apparatus

A document transport apparatus includes a sheet feeding device for feeding a document from a sheet feeding tray; a transport device for receiving the document from the sheet feeding device and transporting the document to a predetermined position on a platen of an image reading apparatus; a sheet discharging device for discharging the document to a sheet discharging tray; a switch back path for turning the document upside down and reversing a front end and a rear end thereof, and for subsequently guiding the document to the sheet discharging device; and sheet discharging path for turning the document upside down, and subsequently guiding the document to the sheet discharging device. A control device controls such that the document is transported to the switch back path and returned from the switch back path to the platen via the sheet discharging path.