PURPOSE: To improve an operating efficiency of a freezer by a method wherein the freezer is provided with a check valve connected between a discharging part and a condensor, a differential pressure valve connected between the condensor and a capillary tube and a differential pressure capillary tube connected between the discharging part of a compressor and the check valve.

CONSTITUTION: A condensor 2 is connected to a discharging part of a low pressure type rotary compressor 1 through a check valve 5. A capirally tube 3 is connected to an outlet port of a condensor 2 through a differential pressure valve 6 and at the same a differential pressure capillary tube 7 is connected between a differential pressure feeding part 6a, the compressor 1 and the check valve 5. When it is assumed that a value of reference differential pressure is defined as A, a relation of ΔP ≤ A is in its normal state, the differential pressure valve 6 is opened, refrigerant is flowed from the condensor 2 toward an evaporator 4 and in turn when a relation of ΔP ≥ A is attained, the differential pressure valve 6 is closed and operated, thereby a flow of high pressure refrigerant from the condensor 2 to the evaporator 6 is shielded to restrict an increased temperature of the evaporator 6.