An outer tube part 8 and an inner tube part 6 which is disposed in an interior of the outer tube part 8 are provided in an air-conditioning duct system which is connected to an air flow path downstream side of a vehicle air-conditioning system, and a side branch type silencer chamber 9 is defined by an inner circumferential surface of the outer tube part 8 and an outer circumferential surface of the inner tube part 6. In addition, an axis of at least a portion of the outer tube part 8 which confronts the inner tube part 6 and an axis of the inner tube part 6 are both made to be a straight line, and a register functioning part is provided in an interior of a portion of the outer tube part 8 which lies further downstream in an air flow path than the inner tube part 6.