An air conditioner includes: a first heat exchanger disposed indoors; a second heat exchanger disposed outdoors and connected to the first heat exchanger; a water tank for accommodating water for generating steam; a filtering device for filtering indoor air; a first valve, which guides, to the water tank, the water for generating steam or guides, to the outdoors, remaining substances generated in the filtering device or condensate water generated in the first exchanger; and a second valve which is connected to the first valve by means of a connecting pipe, and which receives the water for generating steam or discharges the remaining substances or the condensate water transferred from the first valve.