To provide a method and device for detoxifying PCB-containing insulating oil, to prevent a scale from adhering onto the inner wall surface of a reaction tank when dechlorinating and detoxifying PCB to be contained in insulating oil through the use of metallic sodium.

In the method for detoxifying the PCB-containing insulating oil, the PCB to be contained in the insulating oil is dechlorinated and detoxified through the use of the metallic sodium. In the method, the oil to be processed is the PCB-containing insulating oil containing an oil oxidation alteration product. An anti-adhesive agent to prevent a reaction product to be produced in detoxifying the oil to be processed from adhering onto the inner wall surface of the reaction tank is added to the reaction tank 17, thereby to detoxify the oil to be processed by reacting the metallic sodium with the PCB. It is preferable that the wall surface of the reaction tank 17 and the front surfaces of stirring blades 27 and a stirring axis 29 are coated with fluororesin.