A lubricating oil from an oil supply pipe is supplied to a pump chamber (2A) through an axial direction oil supply hole of an oil supply passage, a diameter direction oil supply hole, and an axial direction oil supply groove. A gas passage includes a diameter direction gas hole and an axial direction gas groove, and the diameter direction gas hole is made to communicate with the axial direction gas groove when the diameter direction oil supply hole is made to communicate with the axial direction oil supply groove. When a passage area of the gas passage is defined as S 1 , a passage area of the oil supply passage is S 2 , a passage area of the oil supply pipe is S 3 , a diameter of the diameter direction oil supply hole is d 2 , and a width of the axial direction oil supply groove in a rotational direction of a rotor (3) is L, the passage area S 2 of the oil supply passage is set to be in a range of S 1