PURPOSE: To accurately detect a noise signal propagating into a duct without deteriorating it by a turbulent flow noise due to the disturbance and the eddy of air occurring in the duct, to isolate vibration transmitted to a microphone from the inside wall surface of the duct and to reduce the turbulent flow noise occurring caused when the air in the duct collides with the microphone and the peripheral part directly.

CONSTITUTION: This device is provided with two microphones 102 detecting the noise propagating into the duct 101 and a speaker 103 radiating a sound with an amplitude equal to and a phase opposite to the noise detected by the microphones 102, and is constituted so that the sound gathering surfaces 2 of the microphones 102 are provided so as to become the same surface as the inside wall surface 1 of the duct 101 or to be projected from the inside wall surface 1, and porous materials 3 molded in a semispherial shape are covered on the microphones 102 so that the spherical surfaces become the inside of the duct 101.