The present application discloses a diffusion furnace, including: a furnace tube structure including a furnace tube body and a furnace bottom, a bottom of the furnace tube body being connected to the furnace bottom to form a reaction chamber; and a carrying structure including a pedestal and a plurality of cassettes disposed on the pedestal, the pedestal being disposed on the furnace bottom. By disposing the plurality of the cassettes, a height of the furnace tube body can be decreased and a width of the furnace tube body can be increased, thus enlarging a space of equipment repair and maintenance, which is favorable for the repair and maintenance of the equipment.