a duct apparatus which is connected to an air conditioner and has therein a tubular duct through which conditioned air circulates , includes : an opening portion provided in the duct which extends along a flowing direction of the conditioned air which flows in , the opening portion being provided in such a manner as to extend along the flowing direction of the conditioned air ; and a plate - shaped air guiding portion for covering the opening portion , wherein the air guiding portion has a plate thickness of 1 . 0 mm or more , and has a plurality of air guiding holes allowing an interior of the duct to communicate with an outside and arranged along the flowing direction of the conditioned air .