A reflecting plate type silencer pipe including a reflecting plate is provided for reducing a dominant frequency noise passing through a pipeline. Sound waves propagated in the pipeline as a one-dimensional plane wave are divided into two, that is, sound waves advancing straight along the pipeline and sound waves caused to pass through a bypass route by the reflecting plate thereby being delayed in phase. Both of the sound waves are joined again so as to synchronously advance in the same direction and in parallel to each other with the sound waves being the same in amplitude and opposite in phase to each other, and wave interference is effected between the sound waves, whereby wave propagation energy of the sound wave of the frequency to be silenced passing through the pipeline is selectively dissipated.