PURPOSE: To prevent lubricant intruded into negative pressure chamber from further intruding into third check valve side by providing a ventilated gas/liquid separating means in a suction chamber provided in the housing body.

CONSTITUTION: Porous ventilation material 16 for constituting a gas/liquid separating means is contained in a suction chamber R2. Said suction material 16 is made of oily material such as unwoven cloth composed of ulethane foam having continuous foam and various synthetic fibers. Lubricant spray intruded into the negative pressure chamber R1 under high speed driving of vacuum pump trying to flow out through another suction chamber R2 to third check valve V side is adsorved by said ventilation material 16 and blocked from intruding into third check valve V side. Consequently, deterioration of performance of third check valve V is prevented.