An air conditioning apparatus incorporates an ion generating device that generates positive and negative ions by applying an alternating-current voltage between electrodes. The generated positive and negative ions coexist in the air and, when they attach to the surfaces of airborne bacteria, they react chemically with each other and generate radical hydroxyl and hydrogen peroxide, which extract hydrogen atoms from the cells of the bacteria and thereby kill them. This sterilizing effect is combined with the temperature-conditioning, dehumidifying, humidifying, air-purifying, and other functions of the air conditioning apparatus to bring about a comfortable and healthful indoor environment.