Air-conditioning duct system

An air-conditioning duct system which is connected to a downstream side of an air flow path of a vehicle air-conditioning system, comprising:

• a tubular outer tube part;
• a tubular inner tube part which is disposed in an interior of the outer tube part and in which a first inner end, which is an axial end, is integrated with an inner circumferential surface of the outer tube part, a second inner end, which is the other axial end, is disposed further downstream in the air flow path than the first inner end, and an outer circumferential surface of the second inner end and the inner circumferential surface of the outer tube part are spaced apart;
• a side branch type silencer chamber which is defined between the inner circumferential surface of the outer tube part and the outer circumferential surface of the inner tube part;
• and
• a register functioning part having a fin group in which a plurality of fins are aligned and disposed in the interior of the outer tube part in a position lying further downstream in the air flow path than the inner tube part, wherein
• an axis of at least a portion of the outer tube part which confronts the inner tube part and an axis of the inner tube part both constitute a straight line.