Concrete walls play the role not only of the structural material but also of the final barrier of a multiconfinement system of tritium in a fusion reactor or a tritium-handling facility. Therefore, it is required that the behavior of tritium in the concrete materials be clarified to certify the radiation safety of a fusion reactor. The diffusion coefficient of hydrogen in cement paste is obtained by using the permeation experiment in this study, and it is found that the diffusion coefficient of hydrogen in the cement paste is only one order magnitude smaller than the diffusion coefficient of hydrogen in air. Calculation using the diffusion coefficient obtained in this study indicates that the gaseous tritium, HT or T2, can permeate rather rapidly to the outside through the concrete wall of a tritium-handling facility. This calculation implies that installation of a tritium recovery system with proper decontamination performance is required to minimize the tritium transfer to the outer environment.