To efficiently and inexpensively recover a valuable metal or the like contained in combustible waste in a high-quality state by stably burning the waste at a low temperature of 700°C or less.

The heating furnace includes: a heat treatment chamber (5) for receiving the combustible waste (6) which is formed within the furnace surrounded by a furnace wall (3); an air supply path (28) for supplying air into the heat treatment chamber (5); and an exhaust path (30) for discharging waste gas generated in the heat treatment chamber (5) to the outside of the furnace. An air supply amount control unit (34) is provided in the air supply path (28). A heat source housing chamber (8) is provided below the heat treatment chamber (5) within the furnace through an air-permeable first partition plate (7). A liquid recovery chamber (10) is provided below the heat source housing chamber (8) through an air-permeable second partition plate (9). A heat retaining material (12) capable of generating and absorbing heat is disposed within the heat source housing chamber (8). The heat retaining material (12) absorbs heat from the circumferential atmosphere when the internal temperature of the furnace is raised, and releases heat to the circumference when the internal temperature of the furnace is lowered.