To provide an oil-water separator capable of separating seawater containing a large amount of oil at a high speed.

A superconducting magnet is arranged on the outer surface or inner surface of an oily water feeding pipe to provide a magnetic field generation area, and the magnetic field of a flowing direction X is impressed to oily water flowing inside the oily water feeding pipe in the magnetic field generation area. In the meantime, in the magnetic field generation area, a pair of electrodes are disposed on the inner surface of the oily water feeding pipe facing in an orthogonal direction Y to the flowing direction X of the oily water, electromagnetic force in a Z direction orthogonal to the flowing direction X of the oily water is loaded between the electrodes, and conductive water which receives the electromagnetic force and insulating oil which does not receive the electromagnetic force are separated. The electrode includes a body comprising carbon, graphite, a semiconductor, a metal or a water-resistant and conductive carbon-containing resin, and a coating layer of carbon containing at least hydrogen, graphite, diamond-like carbon or/and a carbon-based material of one, two or more of them on a surface to be in contact with the oily water of the body.