To reduce a noise without changing specifications of a device generating a noise and performing modification and to reduce a noise from its opening part without reducing cooling efficiency having an opening part for cooling, generating a noise.

This device 1 has an opening window corresponding to an opening part of a device generating a noise, ducts a-d connected to this opening window open to the outside, and passing through a noise and an air stream, detecting means 4a-4d, 7a-7d detecting sound waves in these ducts a-d converting it into a signal, an opposite phase sound generating sections 5a-5d generating a canceling sound wave being a opposite phase to a noise to cancel a noise based on the signal, and adding sound sources 6a-6d radiating the canceling sound wave into ducts a-d and superimposing a noise. Then, it is mounted at the outside of the device generating a noise and a noise is reduced. Mounting is performed at a space for cooling the surroundings of the opening part of the device generating a noise.