An air conditioner including a housing including a suction panel; a fan disposed inside the housing and configured to generate an air flow which is sucked into the housing through the suction panel to flow in a first direction from upstream to downstream, the suction panel being perpendicular to the first direction; and an electrostatic precipitator disposed inside the housing and including a discharge electrode configured to receive a voltage and to generate ions toward the suction panel, and an upstream electrode disposed upstream of the discharge electrode with respect to the first direction, grounded to form an electric field with the discharge electrode, and disposed between the discharge electrode and the suction panel, wherein at least a portion of the ions generated from the discharge electrode are passed through the suction panel so as to charge aerosols in air outside the housing.