To keep effective cycle of an active fluid by surely allowing it to flow down to a condensing part even when it condenses in a gas pipe, related to a connection end of the gas pipe which is connected to the condensing part.

A rising pipe 28 is formed at a connection end of a gas pipe 16 which is connected to a condenser 12 as a condensing part, with the rising pipe 28 forming a backflow preventing part 30 which is raised to a level higher than the condenser 12. Thus, even if the active fluid condenses in the rising pipe 28, it is forced to flow down to the condenser 12 under gravity.