A tray unit assembly includes a housing, a separating/stacking unit, a tray unit and an elevating member. The separating/stacking unit includes a separating roller unit and a stacking roller unit provided in the housing. The tray unit is provided to be inserted into the housing and includes a first tray body fixed to the housing when the tray unit is inserted into the housing, and a second tray body connected to the first tray body to be slidable in a vertical direction and having a media stacking space formed therein. The elevating member is disposed to be movable up and down and configured to be in contact with a bottom surface of the second tray body to move the second tray body toward the stacking roller unit or the separating roller unit.