an apparatus for separating oil from water , particularly from sea water , having high separating performance , being compact in size so as to be installed in a limited or small space such as a ship , and running at a low cost . the separating apparatus includes a separator in which oil in the water comes up by gravity difference , a flocculating device with a mixer and a flocculant supplying system , the mixer mixing the flocculant and water to attain a flocculation of the suspended material from the separator , a pressurized floating separator for floating and separating the flock under pressure as receiving the fluid from the flocculating device , a gas - liquid mixing - dissolving device taking bubbling water into the fluid which is sent from the flocculating device connected to the lower part of the pressure floating separator , and a filter for removing the remaining oil by passing the fluid from the pressurized separator .