To provide an oil separation system for realizing enhancement of thermal efficiency and capable of eliminating the generation of a water hammer phenomenon.

The oil separation system is constituted such that a vaporization substance containing water vapor and the oil discharged from a cyclone is introduced into a conduit 82 fed with shower of water and is released into a cooled water tank 10 through an aeration pipe 83. The vaporization substance is cooled at a stretch by the shower in the conduit 82 and cooled water in the water tank 10 and is liquefied to water and the oil respectively. In the separation tank 10, separation of both becomes possible by difference in specific gravity of water and oil.