To attenuate noises at the terminal part of a noise input part by positioning the terminal part of the noise input part at the center position of the sphere in the internal space of a structural body and making one part of the structural body a constitution opening toward the outside.

This muffling device is attached to the opening part of an equipment. The noises from the opening part of the equipment pass through a noise input part 4 to be radiated into an internal close space of the device from the terminal part 5 of the noise input part 4. Since the terminal part 5 is positioned roughly at the center position of a hemisphere being equal distances from the sphericality of the hemisphere, noises radiated from this part and reflected on the curved surface gather efficiently at the terminal part 5 and travel equal distances. The phases of these noises reaching by being reflected become phases reverse to phases of noises reaching the terminal part 5 by passing through the noise input part 4 at the same time. Since the sectional area of the terminal part 5 becomes the finite size when it is seen from the curved surface, noises do not coincide with each other correctly but an attenuation effect (muffling efect) near to the effect of interferences due to reverse phases can be expected. Moreover, a structural body 3 has an opening part 6 heading toward the outside.