A clothing treatment device includes a cabinet having an open part provided at the front thereof, a door assembly for opening and closing the open part, a first clothing treatment room, which is provided inside the cabinet so as to provide a space for accommodating clothing therein, and communicates with the outside of the cabinet through the open part, and a machinery room for circulating steam or air in the first clothing treatment room. The door assembly includes an assembly housing which opens and closes the opened front surface of the cabinet and which has a space of a second clothing treatment room therein, and an assembly door for opening and closing, at the front of the cabinet, the second clothing treatment room formed in the assembly housing.