An air conditioning system utilizing outdoor air for cooling an indoor space wherein a rack is disposed, includes at least one rack disposed in the indoor space, the rack having the heating element, an air inlet face and an air discharge face; and at least one air conditioning device using outdoor air for cooling and unitized in accordance with the at least one rack, the air conditioning device having an air supply face and a cold air supply unit for generating cold air and being disposed in vicinity of the rack such that the air supply face faces the air inlet face to form a rack row and an air conditioning device row substantially parallel to the rack row, the rack row being formed of the at least one rack and the air conditioning device row being formed of the at least one air conditioning device.