At the Tritium Process Laboratory (TPL) in the Japan Atomic Energy Research Institute, the Thermal Diffusion process is applied to enrich and recover tritium diluted by the operation and experiments of the other apparatus installed in the gloveboxes. The apparatus is required to process 200-liter of hydrogen isotope mixture containing up to lg tritium by batch operation and enrich tritium to 90%. Preliminary studies were performed numerically as well as experimentally, and good agreement was obtained. Based on the results, the apparatus was designed. Major components are four 2.5m-high diffusion columns, reservoirs, pumps, active metal beds and a mass spectrometer. Whole apparatus was installed in the glovebox in the TPL by the end of 1987. The function of the apparatus was tested with H-D mixtures.