Abstract: A vertical heat treatment apparatus includes a reaction furnace constituted by a reaction chamber having an inner tube and an outer tube and a heater arranged outside the reaction chamber, a manifold communicating with a lower portion of the reaction chamber to support the reaction chamber and a gas being supplied and exhausted through the mainfold, a hollow vessel, arranged together with the boat in the reaction furnace, for supporting a lower end of a boat having objects, and a plurality of first heat-insulating members detachably arranged in the hollow vessel, wherein the number of the first insulating members is adjusted to adjust a heat-insulating effect. The first heat-insulating member includes a fin unit constituted by fins horizontally arranged at predetermined intervals and spacers for keeping the intervals between the fins.