PURPOSE: To reduce noise leaking from an enclosed body by generating canceling sound which cancels noise in a duct port on the basis of a residual noise signal from a residual noise detecting means and a vibration signal from a vibration sensor.

CONSTITUTION: While vibration in an engine 3 is detected by means of a vibration sensor 18, wind speeds in a radiator fan 20 and in an electric fan are detected by means of an exhaust side wind speed sensor and an intake side wind speed sensor individually. On the basis the detected vibration signal from the vibration sensor 18 and a residual noise signal from a residual noise detecting means (microphone) 19 arranged in the vicinity of a duct port 13a in a duct unit 13, canceling sound canceling the noise in the duct port 13a is generated by means of a canceling sound generating means 16. In this way, a reference noise microphone detecting engine noise can be dispensed with, and noise leaking from an enclosed body can be reduced, so that follow-up ability in noise reduction system can be improved.