PURPOSE: To enable a driver in an automobile easily to find out refrigerant leakage by preparing a refrigerant leakage alarm therein.

CONSTITUTION: The pressure in a refrigerating cycle is sensed by a pressure sensing element 2 and detected by a pressure detecting circuit 1. At a pressure-temperature conversion circuit 3 the detected pressure is converted into temperature through the conversion coefficients which have previously been determined by refrigerating cycle volume, normal refrigerant volume, etc. On the other hand, the surrounding temperature of the refrigerating cycle is detected by a heat-sensitive device 4, a temperature detecting circuit 5, and is compared with the temperature converted from the pressure through a comparative circuit 6. If some refrigerant leakage occurs a warning is given by a warning oscillation circuit 7 and an alarm 8 fixed in the automobile. In this way, the refrigerant leakage can easily be found out at the driver seat.