An air conditioner is provided. The air conditioner includes: an indoor device installed at indoor; an outdoor device connected to the indoor device using a refrigerant pipe; a ventilation unit for exchanging heat of outdoor air and indoor air while ventilating indoor air and outdoor air; and a guidance duct for communicating the ventilation unit and an air inhalation portion of the outdoor device in order to guide indoor air exhausted from the ventilation unit to an air inhalation portion faulted in the outdoor device. Therefore, the number of ventilation holes to form in an outer wall of a building can be minimized, a construction cost can be reduced, and performance of the air conditioner can be improved.