A cover unit includes a first cover that is movable between a cover position and an exposed position. A second cover slidably is movable in a direction perpendicular to its visible surface. A cover moving mechanism moves the second cover, wherein, when the first cover is at the cover position, the second cover is at such a height that the visible surface of the second cover is substantially coplanar with a visible surface of the first cover. When the first cover is moved from the cover position to the exposed position, the second cover is moved to such a height such that the visible surface of the second cover is moved by at least an amount that corresponds with the thickness of the first cover. When the first cover is at the exposed position, the first cover is above the visible surface of the second cover.