A raised portion is formed at a predetermined location on an inside surface of a wall portion of an intake manifold. A gas introduction hole for introducing gas containing water vapor is formed in another predetermined location, other than in the raised portion, in the inside surface of the wall portion. An intake air negative pressure outlet hole for releasing intake air negative pressure within the surge tank to the outside is formed in the raised portion. A guide groove which catches moisture that trickles down the inside surface of the wall portion above the raised portion and guides it to a location away from the intake air negative pressure outlet hole, is formed in a region above the intake air negative pressure outlet hole in a rising surface of the raised portion.