PURPOSE: To obtain an improved oil supply system in which mixing of oil into refrigerant gas or generation of cavitation, or the like, in an oil pump can be prevented.

CONSTITUTION: A gear side plate 59 is provided in proximity to the drive gear 31 of a centrifugal compressor while surrounding it. If the gear side plate 59 is not provided, oil is mixed into refrigerant in the form of oil mist and discharged to the outside but, in practice, the gear side plate 59 collects oil and delivers it to a sump 44. In order to prevent cavitation being generated in an oil pump 53 by local stirring in the sump or a mixture of oil and refrigerant gas flowing from the gear side plate 59 side at high speed, a baffle 78 is provided above the oil pump 53 thus preventing flow-in of oil and deflecting the gas mixed with oil to other region of the sump 44.