An air conditioner includes a pipe volume calculating section and a refrigerant circuit configured by the interconnection of a heat source unit and a utilization unit via a refrigerant communication pipe. The pipe volume calculating section calculates the volume of the refrigerant communication pipe based on an additional charging quantity which is a refrigerant quantity to be additionally charged after the refrigerant circuit is configured by interconnecting the heat source unit and the utilization unit via the refrigerant communication pipe.