An experimental apparatus for the developemnt of cryogenic hydrogen isotope separation system (ISS) was designed and fabricated at the Tritium Process Laboratory (TPL) in Japan Atomic Energy Research Institute (JAERI). This apparatus will serve to study the separation characteristics of hydrogen isotope mixture with 104 Ci of tritium. It consists of two distillation columns with isotopic equilibrators for H-D-T mixtures and can be operated with both single column distillation mode and two interlinked cascade modes. Installation of this system in a glovebox was completed by late January, 1988. Tests with tritium will start late 1988.