According to an embodiment, a mold structure comprises an upper mold having a convex portion in a lower surface thereof to press-form a thin aluminum sheet, a lower mold including a main mold part having a forming recess for forming the thin aluminum sheet placed thereon and an auxiliary mold part supporting the main mold part, a back plate spaced apart from an inside of the forming recess and supporting a lower surface of the aluminum sheet, and vacuum generator connected with air passages formed from two opposite sides of the auxiliary mold part to a bottom surface of the forming recess.