An air conditioner that performs a refrigerant quantity judging operation to judge the refrigerant quantity in a refrigerant circuit, comprising: a heat source unit including a compression means configured to compress refrigerant gas and a heat source side heat exchanger; a utilization unit (3a to 3c) including a utilization side heat exchanger (31a to 31c); an expansion mechanism (V2, V9a to V9c); and a first gas refrigerant pipe (46a to 46c, 52, 92) extending from a discharge side of the compression means to the utilization unit; a liquid refrigerant pipe (35a to 35c, 45a to 45c, 51, 91) extending from the heat source side heat exchanger to the utilization unit; characterized in that the air conditioner further comprises: a second gas refrigerant pipe (47a to 47c, 53, 93) extending from a suction side of the compression means to the utilization unit; a switching mechanism (4a to 4c) capable of switching between a first state in which the refrigerant flowing through the liquid refrigerant pipe evaporates in the utilization side heat exchanger and thereafter flows into the second gas refrigerant pipe, and a second state in which the refrigerant flowing through the first gas refrigerant pipe condenses in the utilization side heat exchanger and thereafter flows into the liquid refrigerant pipe; a bypass circuit (27, 43a to 43c) configured to bypass the first gas refrigerant pipe to the second gas refrigerant pipe; a bypass circuit opening/closing means (V3, V13a to V13c) provided in the bypass circuit and configured to open and close the bypass circuit; and a controller configured to open the bypass circuit opening/closing means before performing the refrigerant quantity judging operation. a heat source unit including a compression means configured to compress refrigerant gas and a heat source side heat exchanger; a utilization unit (3a to 3c) including a utilization side heat exchanger (31a to 31c); an expansion mechanism (V2, V9a to V9c); and a first gas refrigerant pipe (46a to 46c, 52, 92) extending from a discharge side of the compression means to the utilization unit; a liquid refrigerant pipe (35a to 35c, 45a to 45c, 51, 91) extending from the heat source side heat exchanger to the utilization unit; a second gas refrigerant pipe (47a to 47c, 53, 93) extending from a suction side of the compression means to the utilization unit; a switching mechanism (4a to 4c) capable of switching between a first state in which the refrigerant flowing through the liquid refrigerant pipe evaporates in the utilization side heat exchanger and thereafter flows into the second gas refrigerant pipe, and a second state in which the refrigerant flowing through the first gas refrigerant pipe condenses in the utilization side heat exchanger and thereafter flows into the liquid refrigerant pipe; a bypass circuit (27, 43a to 43c) configured to bypass the first gas refrigerant pipe to the second gas refrigerant pipe; a bypass circuit opening/closing means (V3, V13a to V13c) provided in the bypass circuit and configured to open and close the bypass circuit; and a controller configured to open the bypass circuit opening/closing means before performing the refrigerant quantity judging operation.