PURPOSE: To provide an air conditioner for a vehicle and the assembling method thereof allowing plural damper shafts to be assembled easily into the divided cases.

CONSTITUTION: An air-conditioning duct 2 is formed by combining one case 13 with the other case 14. In the respective damper shafts 12 of plural dampers 11, one ends 12a are supported by the through bearing parts 15 of one case 13, and the other ends 12b are supported by the cylindrical bearing parts 16 of the other case 14. The height of the respective cylindrical bearing parts 16 is mutually different. At the time of assembling one case 13 to the other case 14, the other ends 12b of the damper shafts 12 are inserted into the cylindrical bearing parts 16 in order from the higher one to assemble the air- conditioning duct 2.