A medium transport unit includes an upstream route in which a print sheet is transported, a first switchback route, a second switchback route, a first guide route, a second guide route, a guide flap configured to switch the route so that the print sheet in the upstream route is transported either toward the first guide route or toward the second guide route, a first discharge route from which the print sheet in the first switchback route is discharged, a second discharge route from which the print sheet in the second switchback route is discharged, and a downstream route passing between the first switchback route and the second switchback route and having an upstream end connected to a junction of downstream ends of the first discharge route and the second discharge route.