A refrigerant system comprising: a refrigerant circuit including a compressor, a heat source side heat exchanger, an expansion mechanism and a utilization side heat exchanger; a temperature adjustment mechanism configured to adjust the temperature of a refrigerant sent during a cooling operation from the heat source side heat exchanger to the utilization side heat exchanger via the expansion mechanism, the temperature adjustment mechanism being located between the heat source side heat exchanger and the utilization side heat exchanger on the refrigerant circuit; a bypass refrigerant circuit into which a portion of the refrigerant sent during a cooling operation from the heat source side heat exchanger to the utilization side heat exchanger is branched, the bypass refrigerant circuit comprising a bypass expansion valve for adjusting the flow rate of the branched refrigerant portion, the branched refrigerant portion passing from the bypass expansion valve to the temperature adjustment mechanism to undergo a heat exchange process with the refrigerant sent from the heat source side heat exchanger to the utilization side heat exchanger, the branched refrigerant portion thereafter being returned to a location at the suction side of the compressor; and a sensor configured to detect the temperature and/or pressure of the refrigerant in the refrigerant circuit or air temperature external to the refrigerant circuit; the refrigerant system further comprising a controller configured to control the opening degree of the bypass expansion valve; and a refrigerant leakage detection sensor configured to detect leakage of the refrigerant from the refrigerant circuit; wherein the controller is configured to adjust the opening degree of the bypass expansion valve as a function of a pressure and/or temperature value detected by the sensor; and wherein the refrigerant system is configured such that, if the refrigerant leakage detection sensor detects refrigerant leakage, the controller is configured to adjust the opening degree of the bypass expansion valve independently of the pressure and/or temperature value detected by the sensor; characterized in that the refrigerant system further comprises a second bypass refrigerant circuit into which a portion of the refrigerant sent during a cooling operation from the temperature adjustment mechanism towards a utilization side expansion valve is branched, the second bypass refrigerant circuit comprising a second bypass valve, and the second branched refrigerant portion being returned to the suction side of the compressor; and wherein the refrigerant system is configured such that, if the refrigerant leakage detection sensor detects refrigerant leakage, the controller is configured to close the second bypass valve. a refrigerant circuit including a compressor, a heat source side heat exchanger, an expansion mechanism and a utilization side heat exchanger; a temperature adjustment mechanism configured to adjust the temperature of a refrigerant sent during a cooling operation from the heat source side heat exchanger to the utilization side heat exchanger via the expansion mechanism, the temperature adjustment mechanism being located between the heat source side heat exchanger and the utilization side heat exchanger on the refrigerant circuit; a bypass refrigerant circuit into which a portion of the refrigerant sent during a cooling operation from the heat source side heat exchanger to the utilization side heat exchanger is branched, the bypass refrigerant circuit comprising a bypass expansion valve for adjusting the flow rate of the branched refrigerant portion, the branched refrigerant portion passing from the bypass expansion valve to the temperature adjustment mechanism to undergo a heat exchange process with the refrigerant sent from the heat source side heat exchanger to the utilization side heat exchanger, the branched refrigerant portion thereafter being returned to a location at the suction side of the compressor; and a sensor configured to detect the temperature and/or pressure of the refrigerant in the refrigerant circuit or air temperature external to the refrigerant circuit; the refrigerant system further comprising a controller configured to control the opening degree of the bypass expansion valve; and a refrigerant leakage detection sensor configured to detect leakage of the refrigerant from the refrigerant circuit; wherein the controller is configured to adjust the opening degree of the bypass expansion valve as a function of a pressure and/or temperature value detected by the sensor; and wherein the refrigerant system is configured such that, if the refrigerant leakage detection sensor detects refrigerant leakage, the controller is configured to adjust the opening degree of the bypass expansion valve independently of the pressure and/or temperature value detected by the sensor; characterized in that the refrigerant system further comprises a second bypass refrigerant circuit into which a portion of the refrigerant sent during a cooling operation from the temperature adjustment mechanism towards a utilization side expansion valve is branched, the second bypass refrigerant circuit comprising a second bypass valve, and the second branched refrigerant portion being returned to the suction side of the compressor; and wherein the refrigerant system is configured such that, if the refrigerant leakage detection sensor detects refrigerant leakage, the controller is configured to close the second bypass valve.