A medium stack tray comprises a stacking member that stacks a sheet medium and is configured to be wound in a roll, a winding mechanism that winds the stacking member, a regulating mechanism that regulates the stacking member being pulled out to be wound by the winding mechanism, anda releasing mechanism that releases regulation for winding the stacking member by the regulating mechanism.In the stacking member being pulled out, at least a portion of a cross section thereof, in a perpendicular direction to a pull-out direction of the stacking member, has a curved shape.Alternatively, the stacking member is configured to have greater minimum area moment of inertia of a cross section when pulled out, than when wound up.