A vacuum pump having a rotary shaft that is rotated by a drive source has a main pump and a sub pump. The main pump includes a pump chamber and a gas transferring body that is located in the pump chamber. The main pump is driven by the drive source through the rotary shaft for transferring gas to an exhaust space. The sub pump is connected to the exhaust space for partially exhausting the gas from the exhaust space. The sub pump is driven by the same drive source. The displacement volume of the sub pump is smaller than that of the main pump.