An intake duct for introducing outside air into an air cleaner of an internal combustion engine is provided which includes a hollow duct body with an opening, and a piece of non-woven fabric, formed in a flat shape, is joined to the duct body to close the opening. The duct body includes a circumferential wall formed of a resin, and the opening is formed along a plane extending through a portion of the circumferential wall. The piece of non-woven fabric is fixed to the duct body so that some of the resin of the duct body penetrates into the non-woven fabric.