In vehicle air-conditioning devices including a refrigerant circuit having a compressor, an outdoor heat exchanger, an expansion device, and an indoor heat exchanger that are connected by refrigerant pipes to form a refrigeration cycle; an indoor air-sending device that supplies air to the indoor heat exchanger; and an outdoor air-sending device that supplies air to the outdoor heat exchanger, the refrigerant circuit is installed under the floor of a vehicle and uses carbon dioxide as the refrigerant.