PURPOSE: To put a soundproof chamber into a sufficient silent state by arranging sound shielding walls in front of the open surface part of the soundproof chamber and outputting the sounds of the antiphase from the phase of the noises to the periph eral parts of these sound shielding walls and silencing the soundproof chamber.

CONSTITUTION: The peripheral parts of the sound shielding walls 3 are provided with an active silencer consisting of microphones 5, digital filters 7 and speakers 9 of sound sources for silencing. Plural pieces of the microphones 5 and the speakers 9 are disposed in the positions corresponding to each other on both the front and rear surfaces of the respective sound shielding walls 3. In such a case, the characteristics of the digital filters are so set that the sounds generated by the speakers 9 are diffracted by the sound shielding walls 3 so as to negate the noises propagating in the soundproof chamber 1, i.e., the noises of low-frequencies by sound wave interference. The high-frequency components of the noise heading from the noise source toward the silencing chamber 1 are shut off by the sound shielding walls 3 and the low-frequency components are attenuated by the sound wave interference with the sounds from the speakers 9, by which the sufficient silencing effect is obtd. in the silencing chamber 1.