A method of treating oil sludge and an apparatus for carrying out same, whereby oil of good quality and inorganic harmless slag can be easily obtained. The method includes agitating oil sludge in an electrolytic tank so as to liquefy same, extracting waste fluid from the liquefied oil sludge, separating solid material from the liquefied oil sludge with a centrifugal separator, extracting waste fluid including the solid material, transporting the liquefied oil sludge to a precipitation tank, extracting waste fluid which is separated and precipitated in the precipitation tank, applying low frequency oscillation to the oil sludge in fluid supply tubes between the electrolytic tank, centrifugal separator and precipitation tank so as to increase oxygen content, extracting oil from an upper portion of the precipitation tank, and incinerating the extracted waste fluid. The apparatus includes an agitator disposed inside an electrolytic tank, a first fluid supply tube connecting the electrolytic tank and a centrifugal separator, a second fluid supply tube connecting the centrifugal separator and a precipitation tank, an oil supply tube connecting the precipitation tank and the oil tank, coils disposed on the first and second fluid supply tubes for applying a low frequency/low voltage/low current signal, and extracting tubes respectively connected between the electrolytic tank, the centrifugal separator and the precipitation tank for extracting waste fluid.