To realize the recovery of a whole amount of PCB-containing insulating oil of a transformer or the like and the utmost reutilization of the recovered insulating oil.

An insulating oil recovering and regenerating method comprises a first process of perfectly extracting the PCB-containing insulating oil, which is washed off from a transformer after insulating oil is drawn out of the transformer by a supercritical fluid circulating pipeline type extraction system using a supercritical fluid CO2 as a solvent, from flocs or an iron core having adsorbed the PCB-containing insulating oil and a second process wherein the obtained extract and the drawn-out insulating oil are subjected to superitical hydroxylation reaction at a temperature of about 380°C slightly higher than the critical temperature of water under the addition of alkali in a vertical circulating pipeline type surpercritical hydroxylation reaction system 27 to generate only the dechlorination of PCB and the insulating oil is treated without being oxidized and thermally deteriorated and the treated insulating oil is separated into upper non-deteriorated oil and lower deteriorated oil to recover only the non-deteriorated oil.