To absorb reflected sound by standing a tubular frame having diameter substantially equal to the minimum width of an air conditioner or a square frame having length of one side substantially equal to the minimum width around the upper air outlet of housing thereby preventing upper diffusion of wind breaking sound and moderating current velocity of blow-up air flow.

A wide opening muffler hood 10 standing around an air outlet 4 opening to the upper surface 3 of a unit comprises a secured square frame 11 having width equal to the minimum width of housing. An acoustic material, e.g. a sponge, or a punching plate may be pasted to the inner surface 12 of the frame. A muffler panel 7 comprising a PVC plate may be arranged in U- shape on the maximum noise generating plane, i.e., on the suction side 2. The interval W3 depends on the body size and it is normal 0.8 m or above. When a plurality of air outlets 4 and fans 5 are provided above the housing, inside of the frame 11 is sectioned by a partition wall 13 to constitute wide opening muffler hoods for individual fans.