To provide an oil and water separation apparatus capable of performing high-speed treatment up to a low oil concentration even when a treatment tank of an oil and water separation apparatus according to a flotation method is compact.

The oil and water separation apparatus causes oil content in the liquid to be treated to float and performs oil and water separation by mixing and dissolving air into the liquid to be treated which is to be fed to the treatment tank 11, ejecting the liquid to be treated in which air is mixed and dissolved into liquid to be treated in the treatment tank 11 and supplying air which is mixed and dissolved in the liquid to be treated in the treatment tank 11 as air bubbles. A nozzle 33 is used for ejecting the liquid to be treated in which air is mixed and dissolved into the liquid to be treated in a first treatment tank 81, and a nozzle 47 is disposed for ejecting the liquid to be treated containing fine air bubbles in the first treatment tank 81 into the liquid to be treated in a second treatment tank 82, wherein two treatment tanks are communicated with each other in the neighborhood of the surface of the liquid to be treated.