PURPOSE: To obtain a refrigeration system having an economizer cycle in which the need of float valve is eliminated in a flash tank by controlling refrigerant flow from a condenser to a flash tank through a liquid supercooling valve and controlling the refrigerant flow from the flash tank to an evaporator through a temperature automatic expansion valve.

CONSTITUTION: A flash tank 32 is disposed between the condenser 26 and the evaporator 40 of a refrigeration system 10, and a liquid supercooling valve 30 is disposed between the flush tank 32 and the condenser 26. Refrigerant flow from the condenser 26 to the flush tank 32 is controlled to keep the supercooling degree of refrigerant at a specified level by opening/closing the liquid supercooling valve 30. Refrigerant flow from the flash tank 32 to the evaporator 40 is controlled through a suction heating temperature automatic expansion valve 38. According to the structure, no float valve is required in the flash tank 32.