PURPOSE: To prevent discharge of gas in a reaction container to the open air even when the gas leaks by a method wherein a react part and a vaporizing and condensing part are mounted to a closed reaction pipe disposed in a heating medium in a chemical reactor, and reversible reaction can take place between the reaction part and the vaporizing and condensing part.

CONSTITUTION: During reaction, for example, a heating medium A becomes a heating medium for heating, and a heating medium B becomes a heating medium for heating. The heating medium for cooling is heated by means of the heating medium B and vaporized to produce gas, which flows through a filter 20 of a partition part 18 and is guided to a reaction part 16 and reacts to a reaction material 6. Heat generated in this case is cooled by means of the heating medium A. Meanwhile, during reversible reaction, the heating medium A becomes a heating medium for heating, and the heating medium B becomes a heating medium for cooling. Reaction gas generated as a result of the reaction material 6 being heated flows through the filter 20 and is guided to a vaporizing and condensing part 17 and cooled by means of the heating medium B for condensation and liquefaction. As noted above, when, during reaction and during reversible reaction and during a stop, reaction gas leaks from a reaction container 14, the reaction gas is not discharged in the open air but in the heating medium.