An image reading device includes a document tray, a linear conveyance path, a curved conveyance path, a document conveyance device, a scanning device, a length detecting device, an operation device, and a controller. A plurality of conveyance rollers are disposed at a predetermined first interval in the linear conveyance path. In the curved conveyance path, a plurality of conveyance rollers are disposed at a predetermined second interval longer than the first interval. When accepting through the operation device an instruction for conveying an original document through the curved conveyance path, the controller allows conveyance of the original document through the curved conveyance path when a length of the original document detected by the length detecting device is not shorter than the second interval or disallows conveyance of the original document through the curved conveyance path when the detected length of the original document is shorter than the second interval.