A tritium removal device for a lithium loop comprises a neutron source (1) for colliding proton on a lithium flow, thereby generating neutrons, a lithium tank (11) for letting the lithium passing through this neutron source (1) to flow into through a flow passage (9), thereby for temporality accumulating it therein, and a lithium pump (17) for circulating and supplying the lithium of this lithium tank (11) to the neutron source (1) through a supply-side flow passage (9′). The lithium tank (11) and the lithium pump (17), into which hydrogen gas containing tritium therein can be easily collected, are enclosed within a hermetically sealed container (7) including an inactive gas therein, so that even if the hydrogen gas including the tritium therein is leaked into the hermetically sealed container (7), it is removed by a hydrogen isotope removal filter. It is possible to remove the tritium, with safety, without diffusing the tritium from an inside of the lithium loop for forming a target flow into an atmosphere.