PURPOSE: To enhance the efficiency of cooling for oil and a pump body by laying a bypass pipe line by which oil is led from an oil tank and is then returned into the tank, and by passing the bypass pipe line trough a working space of a means for cooling the pump body.

CONSTITUTION: A vacuum pump such as an oil rotary pump has a pump body 10 and an oil feed pump 20 which are stored in a pump casing 30 as an oil tank. Meanwhile, a cooling fan 40 for cooling the pump body 10, and a motor 50 for rotating the pump body 10, an oil feed pump 20 and the cooling fan 40 are provided outside of the casing 30. In this arrangement, during operation of the feed pump 30, oil (a) is fed into the pump body 10 from the oil feed pump 30, and fresh oil (a) is introduced through an oil introduction port 21. Further, the fresh oil (a) is fed into a oil cooling pipe 22 provided outside of the pump casing 30 so that the oil is efficiently cooled by the cooling fan 40. Further, it is possible to define a vacuum space with less oil vapor.