The present invention relates to a silencer easily cleanable inside. This silencer comprises a casing cylinder and a segment member housed in the casing cylinder to constitute a sound reducing means. The silencer further comprises a segment member fastening means for fastening the segment member to the casing cylinder, a gas inlet-side lid plate with a punched hole, which closes an opening at one end of the casing cylinder, and a gas outlet-side lid plate with a punched hole, which closes an opening at the other end of the casing cylinder. At least either one of the gas inlet-side lid plate or the gas outlet-side lid plate is adapted to be detachable from the casing cylinder.