An air conditioning system suppresses energy consumption by efficient shared use of air in a common space that is not subjected to air conditioning in an indoor area, among a plurality of air conditioners for the purpose of heat exchange. A plurality of air conditioners each include: a usage-side heat exchanger configured to carry out heat exchange with air in an air-conditioning target space; a heat source-side heat exchanger configured to carry out heat transfer to and from the usage-side heat exchanger; and a heat source-side fan configured to feed air from a common space to the heat source-side heat exchanger and to blow the air into the common space. The heat source-side heat exchangers of the air conditioners are disposed in the common space. A first ventilation fan whose airflow volume is changeable is disposed near an exhaust port through which air is discharged from the common space toward an outdoor area. A controller changes the airflow volume of the ventilation fan, based on information on an air temperature of the common space.