An air conditioner which includes a plurality of indoor units to cool air of a plurality of rooms. Included is a plurality of branch refrigerant lines that each include a backflow prevention part provided at an end of the branch refrigerant line and/or a pulsation dampening part provided at an end of the branch refrigerant line, adjacent to the main refrigerant line. The air conditioner acts to prevent a liquid part of the refrigerant from flowing in a reverse direction into idle indoor heat exchangers. Furthermore, because a pressure pulsation of the refrigerant is dampened by the pulsation dampening part before the refrigerant is supplied into the indoor heat exchangers, the air conditioner reduces vibration, and, thus, noise from the indoor heat exchangers which is caused by the pressure pulsation of the refrigerant.