A duct main body is formed into a hollow tubular shape having in an interior thereof an intake passageway for introducing outside air into an internal combustion engine by connecting integrally a plurality of divided bodies such as a first divided body and a second divided body which are formed of a thermoplastic resin and has in a duct wall of the second divided body an opening which establishes a communication between the inside and outside of the intake passageway. An air-permeable member is insert molded in the second divided body in such a manner as to cover the opening. The air-permeable member has on an outer edge thereof a joining portion which is impregnated with the thermoplastic resin. The second divided body has in at least part of an inner peripheral edge of the opening a vertical wall portion which protrudes outwards from the duct wall of the second divided body along an inner edge of the opening, and at least part of the joining portion of the air-permeable member is embedded in the vertical wall portion in such a manner as to be held therein in a thickness direction.