Abstract: A retort furnace designed for heat and heat and chemical treatment in protective gas atmosphere, process gas atmosphere or in vacuum, equipped with a retort with a lid, made of steel or heat-resisting or creep-resisting alloys, separating the process atmosphere from the ambient atmosphere, with heating elements and thermal insulation outside the retort and with a cooling system. The radiation screens, in the form of at least two metal boards, are installed at supports located at the lid inside the retort; the heating elements are located behind the radiation screens, on the retort side and are separated with the metal screen. A few radiation sealing rings are placed in the extreme area of the brackets. The radiation screens and sealing rings, as well as the circumferential sealing rings permanently fixed in the casing of retort make up the system of reducing heat losses through radiation at the wall of the retort.