A medium transporting apparatus comprising: an adsorption mechanism configured to adsorb a medium to an annular transport belt; a rotation mechanism to rotate the transport belt in a first rotation direction or a second rotation direction that is opposite to the first rotation direction; a first stacker on which the medium transported by the transport belt can be stacked; wherein the adsorption mechanism is configured to adsorb a second surface that is opposite to a first surface of the medium on the stacker side; wherein after rotating the transport belt, to which the medium is adsorbed, in the first rotation direction to transport the medium in a first transport direction, the rotation mechanism is configured to rotate the transport belt in the second rotation direction to transport the medium in a second transport direction so as to stack the medium on the stacker; the medium transporting apparatus characterized by further comprising: a flap that has a swinging support point on an upstream side in the first transport direction; and is swingable between a first position not intersecting an adsorption surface to which the medium is adsorbed in the transport belt when viewed from a width direction that is perpendicular to the first transport direction and a second position intersecting the adsorption surface; and a pressing member that presses the flap toward the second position, wherein the flap includes a first flap surface that is in contact with the first surface of the medium transported in the first transport direction, when the flap is located in the first position, and a second flap surface that is in contact with the second surface of the medium transported in the second transport direction, when the flap is located in the second position, and wherein when a rotation direction of the transport belt is switched from the first rotation direction to the second rotation direction, the second flap surface is disposed at the second position, and the medium transported in the second transport direction is detached form the transport belt. an adsorption mechanism configured to adsorb a medium to an annular transport belt; a rotation mechanism to rotate the transport belt in a first rotation direction or a second rotation direction that is opposite to the first rotation direction; a first stacker on which the medium transported by the transport belt can be stacked; wherein the adsorption mechanism is configured to adsorb a second surface that is opposite to a first surface of the medium on the stacker side; wherein after rotating the transport belt, to which the medium is adsorbed, in the first rotation direction to transport the medium in a first transport direction, the rotation mechanism is configured to rotate the transport belt in the second rotation direction to transport the medium in a second transport direction so as to stack the medium on the stacker; the medium transporting apparatus characterized by further comprising: a flap that has a swinging support point on an upstream side in the first transport direction; and is swingable between a first position not intersecting an adsorption surface to which the medium is adsorbed in the transport belt when viewed from a width direction that is perpendicular to the first transport direction and a second position intersecting the adsorption surface; and a pressing member that presses the flap toward the second position, wherein the flap includes a first flap surface that is in contact with the first surface of the medium transported in the first transport direction, when the flap is located in the first position, and a second flap surface that is in contact with the second surface of the medium transported in the second transport direction, when the flap is located in the second position, and wherein when a rotation direction of the transport belt is switched from the first rotation direction to the second rotation direction, the second flap surface is disposed at the second position, and the medium transported in the second transport direction is detached form the transport belt.