Abstract: A medium supply device includes: a stacking unit in which media are stackable in a vertical direction; a first regulating unit that is provided on the stacking unit and that regulates positions of side portions of the media in a width direction; a supply unit that supplies air to more than one of the media stacked on the stacking unit so that the more than one of the media are raised and separated from each other; a transport unit that successively feeds the media that are raised and separated from each other by the supply unit; a detection unit that detects conditions of the media that are raised and separated from each other by the supply unit from outside in the width direction; a second regulating unit that is attached to an upper section of the stacking unit when the media stacked in the stacking unit are second media and that regulates positions of side portions of the second media in the width direction, the second media having a smaller dimension than first media in the width direction; and a moving u