PURPOSE: To perform the automatic ON/OFF control of a noise control device.

CONSTITUTION: This active noise control device detecting the residual sound being the result of the interfernce between a noise and a canceling sound as an error signal and forming the canceling sound so that the error signal becomes minimum has a band-pass filter 10 provided for allowing the frequency hand of the noise to pass through an amplifier 3 connected with a microphone 2 and for forming a canceling signal and a first detecting circuit 11 detecting a level by comparing the level of the output signal of the band-pass filter 10 being the later among the amplifier 3 and the band-pass filter 10 whose powers are directly supplied frown a power source with a prescribed value. A power ON/OFF circuit 12 connected with the first level detecting circuit 11 performs power supplies to parts whose power supplies are controlled among the active control device other than the amplifier 3 and the band-pass filter 10 in the case the level of the output signal is equal to or larger than the prescribed value and stops power supplies to the parts whose power supplies are controlled in the case the level of the output signal is smaller than the prescribed value.