An air-conditioning apparatus configured to supply conditioned air to a room through an air supply duct by operating an air-sending device, the air-conditioning apparatus comprising: a housing having an outside air port, an air supply port, a return air port, and an exhaust port, the outside air port adapted for taking outside air into the housing, the air supply port adapted for supplying the outside air taken into the housing from the outside air port to the room, the air supply duct being connected to the air supply port, the return air port adapted for taking air into the housing from the room, the exhaust port adapted for exhausting the air taken into the housing from the return air port to an outside; an outside air passage formed in the housing configured to make the outside air port and the air supply port communicate with each other; an exhaust air passage formed in the housing in a separated manner from the outside air passage configured to make the return air port and the exhaust port communicate with each other; an indoor heat exchanger disposed in the outside air passage, comprising a refrigerant adapted for flowing through the indoor heat exchanger; the air-sending device disposed in the outside air passage, and configured to generate an air flow directed toward the room from the outside air port via the air supply port and the air supply duct during operation; and an air supply damper configured to open and close the air supply port, the air supply damper being configured to be open during the operation of the air-sending device and being configured to be closed during a stop of the air-sending device the air-conditioning apparatus being characterised by comprising an open port formed in the housing configured to cause the outside air passage to be open to the outside; and an open port damper configured to open and close the open port, wherein the open port damper is configured to be closed during the operation of the air-sending device, and is configured to be open during the stop of the air-sending device. a housing having an outside air port, an air supply port, a return air port, and an exhaust port, the outside air port adapted for taking outside air into the housing, the air supply port adapted for supplying the outside air taken into the housing from the outside air port to the room, the air supply duct being connected to the air supply port, the return air port adapted for taking air into the housing from the room, the exhaust port adapted for exhausting the air taken into the housing from the return air port to an outside; an outside air passage formed in the housing configured to make the outside air port and the air supply port communicate with each other; an exhaust air passage formed in the housing in a separated manner from the outside air passage configured to make the return air port and the exhaust port communicate with each other; an indoor heat exchanger disposed in the outside air passage, comprising a refrigerant adapted for flowing through the indoor heat exchanger; the air-sending device disposed in the outside air passage, and configured to generate an air flow directed toward the room from the outside air port via the air supply port and the air supply duct during operation; and an air supply damper configured to open and close the air supply port, the air supply damper being configured to be open during the operation of the air-sending device and being configured to be closed during a stop of the air-sending device the air-conditioning apparatus being characterised by comprising an open port formed in the housing configured to cause the outside air passage to be open to the outside; and an open port damper configured to open and close the open port, wherein the open port damper is configured to be closed during the operation of the air-sending device, and is configured to be open during the stop of the air-sending device.