A heat-treating apparatus includes a furnace for heat-treating wafers, installed so as to set its longitudinal direction vertically and having an opening which is formed in its lower end so as to allow a boat having semiconductor wafers mounted thereon to be loaded, a heat-insulating cylinder on which the boat is placed and which is adapted to keep the boat hot, a lifting unit for lifting and loading the boat and the heat-insulating cylinder into the furnace, and for lowering and unloading them from the furnace, a moving unit for pivoting the heat-insulating cylinder and retracting the cylinder from below the boat, and a handler unit for supporting and vertically moving the boat. After the wafers are heat-treated, the boat is moved downward by the lifting unit. The heat-insulating cylinder is retracted from below the boat by the moving unit while the boat is supported by the handler unit. Subsequently, the boat is further lowered by the handler unit so as to completely remove the boat from the furnace.