Abstract: A structure of foaming die for forming a generally inverted-L-shaped headrest, which is designed to receive and enclose an incomplete headrest unit comprising a hollow trim cover assembly of a generally “inverted L” shape having a horizontal upper portion and a vertical head support portion, and at least one headrest stay extending vertically from the horizontal upper portion. This die structure includes die surface portions workable for receiving and enclosing a whole of the hollow trim cover assembly. A movable die element is movably provided so as to be movable toward and away from an operative position where the movable die element is normally set to receive a back cover surface region of such head support portion, thereby allowing the movable die element to be moved away from the operative position and thus allowing a resulting headrest to be removed from the die subsequent to a foaming process.