The present invention provides a concave part cover that can be easily inserted and be safely secured in a concave part even if tolerances and dimensional errors of the concave part such as a slot or a hole, and of the concave part cover for covering the concave part are large. The concave part cover comprises: a top plate 11 for covering the concave part; and a pair of pressing parts 12A and 12B extending from the top plate 11 and pressing side walls 52A and 52B of the concave part when the pressing parts 12A and 12B are inserted into the concave part. Base ends 15A and 15B of the pressing parts 12A and 12B are positioned at the top plate 11 in such a manner that a distance between the base ends 15A and 15B is shorter than distance W (between the side walls 52A and 52B), and portions of extending parts 16A and 16B of the pressing parts 12A and 12B are formed to project outwards until they are spaced at a wider distance therebetween than the distance W.