An air conditioner comprising: a heat exchanger provided in an indoor unit of the air conditioner; a drain pan configured to receive drain water generated in the heat exchanger; an irradiation unit configured to irradiate the drain pan with ultraviolet rays; and a control unit configured to control ultraviolet intensity of the ultraviolet rays from the irradiation unit, wherein the control unit is configured to control the irradiation unit to emit the ultraviolet rays after a cooling operation, characterized in that: the control unit is configured to control the irradiation unit to emit the ultraviolet rays even during the cooling operation, and wherein the control unit is configured to control the irradiation unit to make the ultraviolet intensity after a cooling operation larger than the ultraviolet intensity during the cooling operation; further comprising a detection unit configured to detect a water level of the drain water, wherein the control unit is further configured to control the irradiation unit to irradiate the drain pan with the ultraviolet rays when an accumulated time during which the water level of the drain water detected by the detection unit is equal to or lower than a predetermined level becomes equal to or longer than a predetermined time during the cooling operation. a heat exchanger provided in an indoor unit of the air conditioner; a drain pan configured to receive drain water generated in the heat exchanger; an irradiation unit configured to irradiate the drain pan with ultraviolet rays; and a control unit configured to control ultraviolet intensity of the ultraviolet rays from the irradiation unit, wherein the control unit is configured to control the irradiation unit to emit the ultraviolet rays after a cooling operation, characterized in that: the control unit is configured to control the irradiation unit to emit the ultraviolet rays even during the cooling operation, and wherein the control unit is configured to control the irradiation unit to make the ultraviolet intensity after a cooling operation larger than the ultraviolet intensity during the cooling operation; further comprising a detection unit configured to detect a water level of the drain water, wherein the control unit is further configured to control the irradiation unit to irradiate the drain pan with the ultraviolet rays when an accumulated time during which the water level of the drain water detected by the detection unit is equal to or lower than a predetermined level becomes equal to or longer than a predetermined time during the cooling operation. the control unit is configured to control the irradiation unit to emit the ultraviolet rays even during the cooling operation, and wherein the control unit is configured to control the irradiation unit to make the ultraviolet intensity after a cooling operation larger than the ultraviolet intensity during the cooling operation; further comprising a detection unit configured to detect a water level of the drain water, wherein the control unit is further configured to control the irradiation unit to irradiate the drain pan with the ultraviolet rays when an accumulated time during which the water level of the drain water detected by the detection unit is equal to or lower than a predetermined level becomes equal to or longer than a predetermined time during the cooling operation.