The present application provides a garment processing device comprising: a cabinet having a cabinet chamber for providing a space in which garments are contained, and a cabinet introduction opening through which the cabinet chamber communicates with the outside; a first door capable of opening or closing the cabinet introduction opening; a door chamber provided on the first door so as to provide a garment containing space separated from the cabinet chamber, the door chamber comprising a chamber upper surface, a chamber bottom surface, a mounting surface connecting the chamber upper surface and the chamber bottom surface, and a mounting hole provided through the mounting surface; a second door provided on the first door and capable of opening/closing the door chamber; a hanger comprising a support body for supporting garments, a fastening portion for detachably fixing the support body in the mounting hole, a fastening portion channel provided in the fastening portion, and a support body channel provided in the support body so as to supply air supplied from the fastening portion channel to garments cradled on the support body; a heat exchange portion comprising a circulation channel for withdrawing air inside the door chamber to the outside of the door chamber and then guiding the air to the fastening portion channel, a fan provided in the circulation channel, and an air processing portion for executing at least one of dehumidification and heating of air introduced into the circulation channel; and a channel switching portion comprising a switching channel for connecting the circulation channel and the door chamber, and a switching valve for controlling the opening/closing of the switching channel.