PURPOSE: To eliminate a need for a silencer for preventing noise, and enhance cleaning effect for the inside of each pipe line by providing a steam recovery pipe which suppresses sound by letting steam flow into the inside of a vacuum container, and also providing a protection plate protecting the inside of the vacuum container.

CONSTITUTION: Sound is suppressed by letting steam which has cleaned each pipe line such as a pipe line 2 for a main steam system and the like, flow in the inside of a condenser 5 using a steam recovery pipe 6. The steam recovery pipe 6 is made out of a porous pipe, and is provided with a protection plate 9 at the vicinity of the outlet of the steam recovery pipe 6 so that small pipes 8 within the condenser 5 will not be damaged by steam rushing in out of the steam recovery pipe 6. After steam which flowed in the inside of the condenser 5, has-been hit against the protection plate 9, it is brought into contact with the outside surface of each small pipe 8, and it is thereby condensed so as to be stored therein. Thus, since noise caused by steam which flows in the inside of a vacuum container after it has cleaned the inside of each pipe line, is suppressed to a great extent, there is thereby no need for installing a silencer for preventing noise.