the tank 9 and the heater 19 for heating the coolant mixture in the tank 9 efficiently gasifies the low boiling coolant correctly controls the quantity of the liquid coolant in the tank 9 and optimizes the ratio between the high and low boiling coolants actually circulating in the refrigerating apparatus according to the operating conditions of the compressor 1 fig9 shows another modification based on the embodiment of fig2 the tank 9 is arranged in a path 15b which is positioned on the suction side of the compressor 1 to pass a gas phase of the coolant mixture a heat transfer tube 41 is wound around the tank 9 an end of the tube 41 is connected to the suction side of the compressor 1 and the other end thereof is connected to a bypass 43 between a first control valve 45 and a second control valve 47 the end of the tube 41 connected to the suction side of the compressor 1 may be connected to a gas injection pipe extending from the compressor 1 a controller 46 controls the opening of each of the first and second control valves 45 and 47 in response to the revolution speed or air conditioning load of the compressor 1 an end of.