An air conditioner comprising an indoor device and an outdoor device, wherein the indoor device includes: a first connector including a first alternating current power terminal L1), a first communication terminal, and a first neutral terminal; a first relay connected between the first AC power terminal and the first communication terminal; and a first communication device connected to the first communication terminal, and wherein the outdoor device includes: a second connector including a second AC power terminal, a second communication terminal, and a second neutral terminal connected, respectively, to the first AC power terminal, the first communication terminal, and the first neutral terminal; a second relay having a first terminal connected to the second communication terminal; a third relay having a first terminal connected to the second AC power terminal; a voltage step-down device and a converter connected to a second terminal of the second relay and a second terminal of the third relay and connected in parallel to each other; a communication voltage output connected to the second terminal of the second relay and the second terminal of the third relay to output a communication voltage; and a second communication device connected between the communication voltage output and the second communication terminal, characterized in that the air conditioner is adapted such that in a state in which an AC power is applied through the first power line connected between the first AC power terminal and the second AC power terminal, when the first relay is turned on, the AC power through the first power line is transmitted to the first communication device and the second communication terminal via the first communication terminal from the first AC power terminal, and wherein, when the second relay is turned on, the AC power through the second communication terminal is transmitted to the voltage step-down device and the converter to operate the voltage step-down device and the converter. a first connector including a first alternating current power terminal L1), a first communication terminal, and a first neutral terminal; a first relay connected between the first AC power terminal and the first communication terminal; and a first communication device connected to the first communication terminal, and wherein the outdoor device includes: a second connector including a second AC power terminal, a second communication terminal, and a second neutral terminal connected, respectively, to the first AC power terminal, the first communication terminal, and the first neutral terminal; a second relay having a first terminal connected to the second communication terminal; a third relay having a first terminal connected to the second AC power terminal; a voltage step-down device and a converter connected to a second terminal of the second relay and a second terminal of the third relay and connected in parallel to each other; a communication voltage output connected to the second terminal of the second relay and the second terminal of the third relay to output a communication voltage; and a second communication device connected between the communication voltage output and the second communication terminal, characterized in that the air conditioner is adapted such that in a state in which an AC power is applied through the first power line connected between the first AC power terminal and the second AC power terminal, when the first relay is turned on, the AC power through the first power line is transmitted to the first communication device and the second communication terminal via the first communication terminal from the first AC power terminal, and wherein, when the second relay is turned on, the AC power through the second communication terminal is transmitted to the voltage step-down device and the converter to operate the voltage step-down device and the converter. a second connector including a second AC power terminal, a second communication terminal, and a second neutral terminal connected, respectively, to the first AC power terminal, the first communication terminal, and the first neutral terminal; a second relay having a first terminal connected to the second communication terminal; a third relay having a first terminal connected to the second AC power terminal; a voltage step-down device and a converter connected to a second terminal of the second relay and a second terminal of the third relay and connected in parallel to each other; a communication voltage output connected to the second terminal of the second relay and the second terminal of the third relay to output a communication voltage; and a second communication device connected between the communication voltage output and the second communication terminal, characterized in that the air conditioner is adapted such that in a state in which an AC power is applied through the first power line connected between the first AC power terminal and the second AC power terminal, when the first relay is turned on, the AC power through the first power line is transmitted to the first communication device and the second communication terminal via the first communication terminal from the first AC power terminal, and wherein, when the second relay is turned on, the AC power through the second communication terminal is transmitted to the voltage step-down device and the converter to operate the voltage step-down device and the converter.