To provide an oil separator for an oil-containing substance, which can safely and efficiently recover oil from an oil-containing substance, and to provide a method of the oil separator for an oil-containing substance.

A cooling step (step S8) to a vaporized substance is performed after a step S7 of performing separation between a gas and a solid by centrifugal separation, collision separation or the like in a cyclone 24 and before a step S10 of returning vaporized oil and water to a liquid with a scrubber 27. In the cooling step (step S8), steam from a steam boiler 2 is fed before feeding to a superheat heater 12, and is heat-exchanged with a vaporized substance circulating through the inside of piping 48, and the steam used for the cooling step (step S8) is jetted to a jet space 43 as superheated steam from the steam boiler 2, thus the efficient utilization of heat is made possible.