Disclosed is an air conditioner including a plurality of units having an outdoor unit and an indoor unit. The plurality of units includes a controller configured to control an input/output and control to operate according to setting and a communication unit configured to transmit and receive data in a wireless communication method between the plurality of units. The communication unit includes a plurality of antenna connection units respectively connected to the plurality of antennas, and a transmission/reception unit configured to apply a signal of a certain frequency band to the plurality of antennas through the plurality of antenna connection units, and to process a signal received from the plurality of antennas. The communication unit includes a plurality of antennas, and is configured to transmit and receive data through multiple input and output, so that the plurality of units can directly communicate wirelessly, specify a frequency of a signal used in consideration of obstacles in a building and installation distances, and perform multiple input and output by using the plurality of antennas, thereby achieving stable communication by securing communication coverage, and improving efficiency and stability according to the management and operation of the air conditioner.