PURPOSE: To provide a device which functions with an improved sound-deadening efficiency and whose deadening effect keeps unabated against soiling such as that of dust.

CONSTITUTION: A silencer consists of a duct for the exhaust or feeding of gaseous matter having a double wall, of which the inner wall consists of a punched plate 8 with through holes 8a opened and the outer wall 7 hermetically covers the duct. The rate at which the through holes are opened in the punched plate 8 and the distance between the inner and outer walls of the double wall are set according to the frequency of the noise that is to be arrested. Furthermore, the sound-deadening effect is enhanced by applying a sound-absorbing material 9, such as glass wool, to the punched plate 8 on the side between the two walls and with some space left from the outer wall 7. Moreover, since the diameter of the through holes in the punched plate and the rate at which they are opened both are set according to the frequency of the noise to be suppressed, distinguishing measures can be taken against noise in a wide variety of cases. Basically the punched plate is designed to effect the silencing, which effect remains good against soiling such as that of dust. Waterproofing work is not required.