A medium transport device includes a positional corrector configured to transport a medium and correct a position of the medium in a width direction of the medium by moving the medium in the width direction, a first inclination corrector disposed on a transport path of the medium and configured to correct an inclination of the medium relative to a transport direction of the medium, and a second inclination corrector configured to correct the inclination of the medium on an upstream side of the first inclination corrector in the transport direction.

A stacker includes a placement part that stacks thereon sheets discharged from a discharge port by a conveyor that conveys the sheets; a side guide that regulates edges of the sheets in a width direction intersecting a discharge direction of the sheets; a guide driver that moves the side guide along the width direction; and a controller configured to control the guide driver to position the side guide at a position where the sheet discharged from the discharge port is supported from below by the side guide.