Hydrogen isotopes are the fuel of fusion reactor. A part of hydrogen isotopes induced into the reactor core will be evaluated by the vacuum pump, and finally induced into the reactor core again after the processes such as purification, isotope separation, and storage. In these fuel cycle, the interaction between hydrogen isotopes and metal materials occurs. Because hydrogen is the smallest element, therefore, they can easily penetrate into metal materials. In this course, we will observe these migration phenomena of hydrogen isotopes in metal materials.