To sufficiently suppress lowering of sound absorption effect and to sufficiently absorb a predetermined design frequency sound, even when particle is mixed into fluid.

This silencer comprises a silencer body, which is disposed in an exhaust duct and an outer surface of a hollow frame structure 40 thereof is covered with a porous plate 5. The hollow frame structure 40 is formed by a latticed combination of horizontal reinforcement plates 3 and perpendicular reinforcement plates 4. In that case, the horizontal reinforcement plates 3 are provided with through holes 6 every latticed block.