PURPOSE: To hold always oil surface properly in running a compressor by arranging two compressors in parallel to supply a portion of gas separated by a separator from lubricating oil to one compressor and the remaining gas to the other compressor and providing a check valve in a pressure and oil equalizing pipe for interconnecting both compression element chambers.

CONSTITUTION: When compressors 1, 2 are run in parallel, oil separated by a separator 5a enters a compression element chamber 2d and is supplied to a compression element chamber 1d through a pressure and oil equalizing pipe 3 and a check valve 4 because of (pressure in motor chamber 2c)>(pressure in motor chamber 1c). In running only the compressor 1, a portion of oil entering a compression element chamber 2d from a suction pipe 5 is supplied to the compression element chamber 1d by the differential pressure between the compression element chambers 2d, 1d. In running only the compressor 2, gas flow from the compressor 1 to the compression element chamber 2d is blocked by the check valve 4 so that oil returned to the motor chamber 2c cannot be sent to the chamber 2d and oil surface is stabilized.