PURPOSE: To improve a silencing effect in a high frequency band largely more than heretofore in an active silencer in which a noise of a noise medium is positively silenced by a secondary sound source.

CONSTITUTION: This device is composed of a microphone 41 arranged at an upstream side of a secondary sound source in a silencer space 35, a delay means 43 delaying an electric signal from the microphone 41 so that phase lag caused by the distance between the secondary sound source 39 and the microphone 41 and intrinsic phase lag of the secondary sound source 39 are dissolved, and an inversion means 47 reversing an electric signal delayed by the delay means 43 and outputting it to the secondary sound source 39. Also, this device is composed of a forward side microphone and an upstream side microphone arranged at forward and upstream of the secondary sound source 39 in a silencer space 35, an addition means adding electric signals from the forward side microphone and the upstream side microphone, and an inversion means reversing an electric signal added by the addition means and outputting it to the secondary sound source 39.