PURPOSE: To simplify the intervention of signal code. Without changing the structure of an engine.

CONSTITUTION: An ANC controller 11 generate a signal with a waveform nearly opposite to the waveform of a noise occurring from the engine based on a reference signal sent from a current-voltage converter 7 and an error signal sent from a microphone 9 and sents it to a speaker 15 through an amplifier 13. The speaker 15 transforms the signal generated by the ANC controller 11 into a sound and sents it into an exhaust duct 5. The noise of the engine 1 is canceled by the sound generated from the speaker 15, but all of the noise are not canceled, and the sound remaining without being canceled is collected by the microphone 9. The controller 11 performs the adaptive control so that the error signal becomes minimum.