The object of the present invention is to provide a stable isotope concentrating device that has high energy efficiency and can reduce equipment costs, and provides a stable isotope concentrating device including a distillation column group in which multiple distillation columns are cascaded, and the distillation column group includes: a tray column group including one or more tray columns; and a packing column group including one or more packing columns, and the packing column group is located on a secondary side of the tray column group.