In a silencer, holes are disposed in one row with intervals to each other along one direction, holes forming the one row are disposed in a plurality of rows in a direction perpendicular to the one direction, and positions of the holes in adjacent rows are shifted in the one direction and disposed in a zigzag pattern. A disposition interval of the holes of an outer edge hole row forming one row in at least two sides opposite to each other in the silencing porous plate is set to be larger than a disposition interval of the holes of a row inside the outer edge hole row.