PURPOSE: To remove both of iron or the like and water included in waste oil and prevent piping or the like in reusing the oil from getting corroded by water by using a filter tank filled with a hydrophobic filter medium combinedly with a magnetic filter tank.

CONSTITUTION: A magnetic medium 6 is filled in a casing 5 of a storage tank 1 for waste oil to be treated, and a magnetic filter 2 for removing iron content in which a permanent magnet 7 is disposed is connected with the outside of the casing 5, with which a filter tank 3 for removing water content constituted of a casing 9 equipped with a hydrophobic filter material 4 is connected forming a waste oil purification device. A magnetic substance and the like such as iron content and the like in the waste oil are removed by exciting the magnetic medium and having the waste oil go through a magnetic filter. The oil flowed out of the magnetic filter is fed into a filter tank filled with a hydrophobic filter medium, where water content is removed. As for the hydrophobic filter medium, a synthetic resin filter medium such as polyethylene, polypropylene or the like is used.