PURPOSE: To eliminate a lack of oil and improve a reliability in operation by a method wherein a freezer device is provided with a check valve and an oil separator connected in series between a discharging part and a condensor, a differential pressure valve connected between the oil separator and a suction side, and a differential pressure capillary tube.

CONSTITUTION: A discharging part 1a of a low pressure type rotary compressor 1 is connected to a condensor 2 through a check valve 5 and an oil separator 6. Oil accumulated at a bottom part of the oil separator 6 is supplied to a differential pressure valve 7 through a pipe 6c. One end of a capirary tube 8 is connected to a differential pressure feeding part 7a of the differential pressure valve 7, and the other end is connected between the compressor 1 and the check valve 5. In the event that a value of reference differential pressure is A, a relation of ΔP≤A is defined as a normal state and the differential pressure valve 7 is closed and in turn when a relation of ΔP≥A is attained, the differential pressure valve 7 is opened for a specified period of time, thereby oil accumulated at the oil separator 6 is returned back to a suction pipe acting as a suction side 1b of the compressor 1 and then the oil once reduced in its volume is supplemented.