An air conditioner that adjusts the temperature in a target space, comprising: a refrigerant circuit configured by the interconnection of a compressor, a heat source side heat exchanger, a utilization side expansion valve (41, 51), and a utilization side heat exchanger (42, 52); a controller configured to adjust the temperature such that the target space temperature is equal to or greater than a predetermined criterion temperature and further configured to judge a refrigerant quantity in the refrigerant circuit; characterized in that the air conditioner has a refrigerant leak detection operation mode in which; the controller is configured to judge whether or not the target space temperature is equal to or greater than the predetermined criterion temperature, and adjusts the temperature such that the target space temperature is equal to or greater than the predetermined criterion temperature by performing a heating operation if the target space temperature is not equal to or greater than the predetermined criterion temperature, the controller is configured to then judge the refrigerant quantity while performing a cooling operation to lower the target space temperature when the target space temperature is equal to or greater than the predetermined criterion temperature by calculating the refrigerant quantity in the refrigerant circuit based on at least one value of operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit and the controller is then configured to judge whether or not refrigerant is leaking by judging the calculated refrigerant quantity with respect to a reference refrigerant quantity. a refrigerant circuit configured by the interconnection of a compressor, a heat source side heat exchanger, a utilization side expansion valve (41, 51), and a utilization side heat exchanger (42, 52); a controller configured to adjust the temperature such that the target space temperature is equal to or greater than a predetermined criterion temperature and further configured to judge a refrigerant quantity in the refrigerant circuit; characterized in that the air conditioner has a refrigerant leak detection operation mode in which; the controller is configured to judge whether or not the target space temperature is equal to or greater than the predetermined criterion temperature, and adjusts the temperature such that the target space temperature is equal to or greater than the predetermined criterion temperature by performing a heating operation if the target space temperature is not equal to or greater than the predetermined criterion temperature, the controller is configured to then judge the refrigerant quantity while performing a cooling operation to lower the target space temperature when the target space temperature is equal to or greater than the predetermined criterion temperature by calculating the refrigerant quantity in the refrigerant circuit based on at least one value of operation state quantity of constituent equipment or refrigerant flowing in the refrigerant circuit and the controller is then configured to judge whether or not refrigerant is leaking by judging the calculated refrigerant quantity with respect to a reference refrigerant quantity.