An air conditioning system using outdoor air has a first heat exchanger, an evaporator, a condenser, and a first fan disposed on the interior side; and a second heat exchanger and a second fan disposed on the exterior side. An expansion valve and a compressor are further provided. An air conditioner has a first piping connected to the evaporator, the condenser, the expansion valve, and the compressor, for circulating a first refrigerant to perform a compression-type refrigeration cycle. An indirect outdoor air cooler has a second piping connected to the first heat exchanger and the second heat exchanger for circulating a second refrigerant to induce a heat exchange in the first heat exchanger between the second refrigerant and the indoor, and to induce a heat exchange in the second heat exchanger between the outdoor air and the second refrigerant.