Disclosed is a refrigeration cycle system wherein a compressor (1) for compressing a refrigerant, a radiator (2) for dissipating heat from the refrigerant discharged from the compressor (1), an expander (3) for expanding the refrigerant from the radiator (2), and an evaporator (5) for evaporating the refrigerant from the expander (3) are sequentially arranged in series. The refrigeration cycle system further comprises a refrigerant flow regulating means for controlling the flow rate of the refrigerant flowing into the expander (3) and a control unit for controlling the compressor (1) and the refrigerant flow regulating means. When operation of the compressor (1) is stopped, the control unit controls the refrigerant flow regulating means and reduces the amount of refrigerant flowing into the expander (3).