A document reading device including an image reader. The image reader includes a first reader to read a first image from a first face of a document fed by a document feeder and a second reader to read a second face of the document. An operation mode is switchable between a normal operation mode in which the image reader is in an operation enabled state and an energy-saving mode in which the image reader is in an operation stop state. In a return from the energy saving mode to the normal operation mode, the image reader performs a start-up operation including a first initial operation for returning the first reader to the normal operation mode and then performs a second initial operation for returning the second reader to the normal operation mode.