In accordance with one aspect of the invention, a folding section of a mobile communication device comprises: an upper cover; a lower cover rotatably connected to a main body and engaged with the upper cover; an engaging portion formed between the upper cover and the lower cover for connecting the upper and lower covers, wherein the engaging portion comprises: a hook part protruding from the inner surface of the upper cover; and a hook engaging part formed at the lower cover facing the upper cover for engaging the hook parts; and a cap inserted into the hook engaging part so as to prevent the hook part from releasing from the hook engaging part.