PURPOSE: To maintain a sound absorbing action on gas holding water, etc., containing dissolved foreign matters for long periods of time by respectively loading a muffling material made up of closed cell bodies on the leeward of a muffling box and an adsolvent having a skelton structure of three-dimensional construction on the windward, with an air way being provided in the central part of the box.

CONSTITUTION: A muffling box 4 is formed monolithically with an air blower 2 on the outlet side of the blower. Inside the muffling box 4, a muffling material 5 made up of closed cell bodies such as polyurethane, etc., is loaded on the leeward with an air way 9 provided in the central part. An adsolvent 6 having a skelton structure of three-dimensional construction is loaded on the windward in the box. The adsolvent 6 holds a paste-like material 7 which has absorbed water and is dried, on its bottom. After a proper interval, maintenance is performed to remove the paste-like material. The adsolvent is, for example, produced by processing polyurethane made of closed cell bodies so as to remove films from the closed cell bodies. The reduction of sound adsorbing action due to absorbtion of water, etc., containing dissolved foreign matters in the gas to be handled can thus be prevented.