A document reading device is capable of facilitating attachment/detachment of a reading unit provided inside a U-shaped document conveying path formed in a document conveying device. The document reading device includes a U-shaped document conveying path extending from a sheet supply tray to a sheet discharge tray through a reading section and a reading unit disposed inside the U-shaped document conveying path, a downstream part of the sheet supply tray on which a document is placed and a guide member provided upstream of the document conveying path to continue from the sheet supply tray and is arranged to be attachable/detachable with respect to the sheet supply tray or document conveying path. The reading unit is removable from inside the U-shaped document conveying path through an opening through which the downstream part of the sheet supply tray and guide member of the document conveying path are removed.