To recover oil and also to unnecessitate frequent replacement of a filter medium by having a filter part provided with a filter medium for adsorbing oil and a storage tank installed below the filter part in which water based washing liquid filtered by the filter part flows and is stored.

A feeding apt 5 is descended to make a packing 20 abut on the upper surface of upper part filter paper 11. Then, when used water based washing liquid is fed to the feeding part 5 by a prescribed quantity, the feeding is stopped. Next, compressed air is fed into the feeding part 5, and the used water based washing liquid passes through the upper part filter paper 11 and a lower part filter paper 12 and drips into a storage tank 3. At this time, fiber and metal powder are stuck on the upper part filter paper 11 and the lower part filter paper 12, and oil is adsorbed onto them. When the used water based washing liquid is emptied for the feeding part 5 to finish one process, the feeding part is ascended, and also the upper part filter paper 11 and the lower part filter paper 12 travel a distance corresponding to the size of an opening 19 and are taken up on take-up rolls 15, 16.