To reduce the quantity of lead and bismuth junked together with used filters when low-melting metals such as lead and bismuth used as a coolant in a reactor, related facilities and the like are purified.

In the reactor 1 and facilities related to it where a liquid low-melting metal M of a lead base is used as a coolant, a high boiling point solution (b) such as glycerin and silicon oil is heated to 125°C to 300°C, the solution (b) heated to the temperature mentioned above is mixed with a liquid or solid low-melting metal M of a lead base containing impurities (c) and then the impurities (c) are separated from the mixture of them and the metal M.