PURPOSE: To increase the quantity of noise reduction in an area where a passenger are present by providing a means which detects the riding position of the passenger and a microphone selection part which selects only the microphone at the position where the passenger is detected, and performing output control over all speakers in each control system.

CONSTITUTION: After an engine is started, the microphone selection part 40 detects the position of the passenger by a passenger position sensor such as a seat belt switch or door switch. When it is decided that passengers sit on all seats, the microphone selection part 40 select; and outputs all microphone output signals and supplies them to front and rear seat controllers 2A and 2B. When a passenger sits on only the driver's seat, on the other hand, a front seat control system does not input the output signal of a microphone MIC 2 to a multichannel arithmetic part as shown by a dotted line and performs adaptive control so that the outputs of speakers SP1 and SP2 become minimum. For a rear seat control system, the rear seat controller 2B performs adaptive control corresponding to the position of the passenger.