The air-conditioning unit includes an air-conditioning case, a heater, a bypass path bypassing the heater, an air-mixing chamber, an air-mixing door, and an air opening. The air-conditioning unit also includes an auxiliary door arranged in series with the air-mixing door in the bypass path. The auxiliary door is operated between at a first position and at a second position. The auxiliary door in the first position closes the bypass path more than in the second position. The auxiliary door is operated at the first position at least when the air-mixing door opens the bypass path slightly.