PURPOSE: To sharply reduce combustion noise by outputting a sound of opposite phase to that of combustion noise from a speaker and utilizing phase interference between sound waves.

CONSTITUTION: There are provided a plurality of first pressure detectors 13 each for detecting pressure in a burner 10, a second pressure detector 14 for detecting pressure outside an exhaust port 12, an evaluation device 15 for evaluating based upon signals from the first and second pressure detectors 13, 14 a sound wave signal where pressure existent in the vicinity of the second pressure detector 14 is suppressed by opposite phase interference due to the sound waves, and a sound attenuation speaker 16 disposed outside the exhaust port 12 for generating the sound wave. Hereby, the opposite phase to that of the combustion noise can be generated on the basis of pressure variations over the whole of the burner NO to sharply reduce the noise sound, and a sound attenuation effect is kept without interruption by generating an opposite phase sound using adaptive control based upon the signal from the second pressure detector 14.