A heat treatment system may include: a heat treatment furnace including an entrance, an exit, and an internal space in which a plurality of saggars is conveyed from the entrance to the exit; and a return line located outside the heat treatment furnace and configured to convey the plurality of saggars from the exit to the entrance. The return line may include: a first conveying device located in a first section and configured to convey the plurality of saggars; and a second conveying device located in a second section different from the first section and configured to convey the plurality of saggars by a beam or a bar.