Abstract: A silencer includes an air passage tube having an air inlet for introducing air thereinto, and a side branch tube connected to the air passage tube and having a closed end for attenuating noise produced by the air introduced into the air passage tube. The side branch tube may be either a flexible tube or have a flexible portion for allowing convenient bending and mounting thereof in the available space. The side branch tube may comprise a pair of different tube portions connected to each other. The side branch tube may have a water drain hole defined in its lowermost portion and preferably the cross-sectional area of the water drain hole is no greater than 1% of the cross-sectional area of the side branch tube. The side branch tube serves to attenuate high-frequency noise and the silencer may additionally include a resonator chamber for attenuating low-frequency noise.