PURPOSE: To obtain an air distributing system for an air conditioner which can be executed easily and inexpensively and is suitable for discrete and disperse type air conditioning, by constructing part or the whole of ducts for feeding conditioned air into rooms to be air- conditioned and air ducts for returning air from the rooms to the air conditioner, as double ducts.

CONSTITUTION: An air-conditioning unit 1 comprising a compressor 1, a heat exchanger 12, a piping 13, a blower 14 and the like sucks air from rooms 4 to be air-conditioned. The air sucked into the unit 1 is subjected to heat exchange with a refrigerant in the heat exchanger 12, and is blown back into the rooms 4. A branch outlet box having a plurality of connecting ports for air ducts is disposed in each of the rooms 4a-4f to be air-conditioned. The branch outlet boxes are connected to the air-conditioning unit 1 by air ducts 31, 32. The boxes are connected to each other by double air ducts 3. The double duct has an inner duct through which conditioned cold air is passed, and an outer duct through which return air coming from each air-conditioned room is passed. Therefore, a heat-insulating treatment is not needed for the double duct, and the duct is easy to handle. Since air is sucked from and blown into each of the rooms 4 directly and individually, no pressure difference is generated between the room being air-conditioned and the exterior of the room. In addition, it is unnecessary to provide each door with an air passage gallery, so that the door can be smoothly opened and closed.