PURPOSE: To prevent the leakage of compressed gas through gaps between rotor shafts and shaft holes and others into a suction port by fitting annular seal materials into annular holes around the rotor shafts.

CONSTITUTION: Annular seal materials 20 and 21 are fitted into annular holes 44 and 45, while O-rings 22 and 23 are fitted between bottoms of the shaft holes 44 and 45 and the annular seal materials 20 and 21, and one end face 46 of the annular seal materials is in contact with discharge side end faces 37 and 38 of rotors 1 and 2. In this construction, gaps 40 and 41 on the discharge side end face are partitioned by the annular seal materials 20 and 21 into an outer space 47 on the side of rotor grooves and an inner space 48 on the side of gaps 42 and 43 between rotor shafts 3 and 4 and bearings 18 and 19 for preventing the leakage of compressed gas from the side of a discharge port 16 to that of roller bearings 9 and 10.