Abstract: A structure for connecting an air-conditioning duct to an air-conditioning unit; the air-conditioning unit 1 having a first air supply outlet 11 and a second air supply outlet 12 adjacent with each other, the air-conditioning duct having a first air passage and a second air passage adjacent with each other, wherein the first air supply outlet 11 and the second air supply outlet 12 include a U-shaped auxiliary wall 2 having a notched part K at one side therearound, a supply outlet boundary wall 130 separating the first air supply outlet 11 and the second air supply outlet 12, and a duct side step part Z is formed between an opening rim of a first duct 31 and an opening rim of a second duct 32, the duct side step part Z is contacted with is contacted with the supply outlet boundary wall 130 to install the air-conditioning duct 2 to the air-conditioning unit 1.