PURPOSE: To make it possible to increase the volume of oil supply upon heavy load operation, by forming a minute hole in a suction port for communicating a low pressure introduction port with the inside of a high pressure vessel so that oil is fed into a cylinder under differential pressure.

CONSTITUTION: High pressure gas is discharged from a discharge port 5b into the pressure vessel 1 after a roller 6 is rotated for compressing gas by introducing low pressure gas into a cylinder 5 through a suction port 5a. For lubricating compressing elements, the cylinder 5 is formed with a minute diameter hole 15 for communicating the suction port 5a with the inside of the pressure vessel 1 so that the oil 9 in the pressure vessel 1 is led directly to the cylinder 5 under differential pressure between a gas pressure in the pressure vessel 1 and a low pressure of gas in the suction port 5a. Further, the bearings 7, 8 are formed with oil guide grooves 7a, 8a for introducing oil into the roller 6 in the vicinity of the gas discharge completion point of the roller 6, thereby oil may be fed to the journal 4b of a crank shaft.