An air conditioner installable on a window frame and having a ventilation function. The air conditioner comprises a cabinet comprising a first inlet hole, a second inlet hole and a third inlet hole, a first heat exchanger provided inside the cabinet to allow indoor air, which is introduced through the first inlet hole, to exchange heat, a second heat exchanger provided inside the cabinet to allow outdoor air, which is introduced through the second inlet hole, to exchange heat, and a third heat exchanger provided inside the cabinet to be located between the first heat exchanger and the second heat exchanger in a height direction of the cabinet, and provided to allow outdoor air, which is introduced through the third inlet hole, and condensed water, which is generated in the first heat exchanger, to exchange heat with each other.