An air conditioner, comprising: a refrigerant circuit configured by the interconnection of a heat source unit and a utilization unit (4, 5); operation controlling means capable of performing a refrigerant quantity judging operation; refrigerant quantity judging means configured to judge the adequacy of a refrigerant quantity in the refrigerant circuit by using an operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit in the refrigerant quantity judging operation; condition setting means configured to set a condition for the refrigerant quantity judging operation according to an information on the utilization unit (4, 5) obtained by an information obtaining means; and refrigerant quantity calculating means configured to calculate a refrigerant quantity in the refrigerant circuit from an operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit in the refrigerant quantity judging operation, by using a relational expression between a refrigerant quantity in the refrigerant circuit and an operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit, wherein the refrigerant quantity judging means is configured to judge the adequacy of the refrigerant quantity in the refrigerant circuit by using the refrigerant quantity in the refrigerant circuit calculated by the refrigerant quantity calculating means, and characterized by a transmission line configured to exchange a signal between the heat source unit and the utilization unit (4, 5); the information obtaining means being configured to obtain information on the utilization unit (4, 5) connected to the heat source unit via the transmission line, wherein the condition setting means is configured to set the relational expression as a condition for the refrigerant quantity judging operation, according to a model of the utilization unit (4, 5) as the information on the utilization unit obtained by the information obtaining means. a refrigerant circuit configured by the interconnection of a heat source unit and a utilization unit (4, 5); operation controlling means capable of performing a refrigerant quantity judging operation; refrigerant quantity judging means configured to judge the adequacy of a refrigerant quantity in the refrigerant circuit by using an operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit in the refrigerant quantity judging operation; condition setting means configured to set a condition for the refrigerant quantity judging operation according to an information on the utilization unit (4, 5) obtained by an information obtaining means; and refrigerant quantity calculating means configured to calculate a refrigerant quantity in the refrigerant circuit from an operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit in the refrigerant quantity judging operation, by using a relational expression between a refrigerant quantity in the refrigerant circuit and an operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit, wherein the refrigerant quantity judging means is configured to judge the adequacy of the refrigerant quantity in the refrigerant circuit by using the refrigerant quantity in the refrigerant circuit calculated by the refrigerant quantity calculating means, and characterized by a transmission line configured to exchange a signal between the heat source unit and the utilization unit (4, 5); the information obtaining means being configured to obtain information on the utilization unit (4, 5) connected to the heat source unit via the transmission line, wherein the condition setting means is configured to set the relational expression as a condition for the refrigerant quantity judging operation, according to a model of the utilization unit (4, 5) as the information on the utilization unit obtained by the information obtaining means.