An air duct of this disclosure includes: a tubular duct body formed from a non-air-permeable material; and a tubular opening end member formed from an air-permeable material. The opening end member is integrated with an end portion of the duct body so as to extend a duct wall of the duct body. D representing a diameter of the opening end member and L representing a length thereof satisfy a relationship 0.1D≦L≦1.5D. An air permeability of the air-permeable material is in a range of 0.3 to 100 sec/300 cc.